Fix first round of trim warnings (#2451)

- DefaultOptionsProvider.TryGetAzureRoleInstanceIdNoThrow use Type.GetType to check for Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment, so the trimmer knows to preserve this type, if it is in the app
- ChannelMessage use the added public API for ChannelReader CanCount and Count, but fallback to reflection on netcoreapp3.1, since those APIs are not available on that runtime.

Contributes to #2449

This at least removes the warnings from using `Microsoft.Extensions.Caching.StackExchangeRedis`.

We could also add a trimming test app as outlined in https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/prepare-libraries-for-trimming#show-all-warnings-with-sample-application, along with a unit test that publishes the app and ensures there are no new warnings. LMK if you think this is valuable.

There are still these warnings left in this library:

```
/_/src/StackExchange.Redis/ScriptParameterMapper.cs(173): Trim analysis warning IL2070: StackExchange.Redis.ScriptParameterMapper.IsValidParameterHash(Type,LuaScript,String&,String&): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors', 'DynamicallyAccessedMemberTypes.PublicMethods', 'DynamicallyAccessedMemberTypes.PublicFields', 'DynamicallyAccessedMemberTypes.PublicNestedTypes', 'DynamicallyAccessedMemberTypes.PublicProperties', 'DynamicallyAccessedMemberTypes.PublicEvents' in call to 'System.Type.GetMember(String)'. The parameter 't' of method 'StackExchange.Redis.ScriptParameterMapper.IsValidParameterHash(Type,LuaScript,String&,String&)' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to. [C:\git\azure-activedirectory-identitymodel-extensions-for-dotnet\test\Microsoft.IdentityModel.AotCompatibility.TestApp\Microsoft.IdentityModel.AotCompatibility.TestApp.csproj]
/_/src/StackExchange.Redis/ScriptParameterMapper.cs(227): Trim analysis warning IL2070: StackExchange.Redis.ScriptParameterMapper.GetParameterExtractor(Type,LuaScript): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors', 'DynamicallyAccessedMemberTypes.PublicMethods', 'DynamicallyAccessedMemberTypes.PublicFields', 'DynamicallyAccessedMemberTypes.PublicNestedTypes', 'DynamicallyAccessedMemberTypes.PublicProperties', 'DynamicallyAccessedMemberTypes.PublicEvents' in call to 'System.Type.GetMember(String)'. The parameter 't' of method 'StackExchange.Redis.ScriptParameterMapper.GetParameterExtractor(Type,LuaScript)' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to. [C:\git\azure-activedirectory-identitymodel-extensions-for-dotnet\test\Microsoft.IdentityModel.AotCompatibility.TestApp\Microsoft.IdentityModel.AotCompatibility.TestApp.csproj]
/_/src/StackExchange.Redis/ScriptParameterMapper.cs(260): Trim analysis warning IL2026: StackExchange.Redis.ScriptParameterMapper.GetParameterExtractor(Type,LuaScript): Using member 'System.Linq.Expressions.Expression.Property(Expression,String)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Creating Expressions requires unreferenced code because the members being referenced by the Expression may be trimmed. [C:\git\azure-activedirectory-identitymodel-extensions-for-dotnet\test\Microsoft.IdentityModel.AotCompatibility.TestApp\Microsoft.IdentityModel.AotCompatibility.TestApp.csproj]
/_/src/StackExchange.Redis/ScriptParameterMapper.cs(261): Trim analysis warning IL2026: StackExchange.Redis.ScriptParameterMapper.GetParameterExtractor(Type,LuaScript): Using member 'System.Linq.Expressions.Expression.Call(Expression,String,Type[],Expression[])' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Creating Expressions requires unreferenced code because the members being referenced by the Expression may be trimmed. [C:\git\azure-activedirectory-identitymodel-extensions-for-dotnet\test\Microsoft.IdentityModel.AotCompatibility.TestApp\Microsoft.IdentityModel.AotCompatibility.TestApp.csproj]
```

Fixing those will require a bit more work, as the whole LuaScript functionality looks like it needs to be marked `RequiresUnreferencedCode`.

cc @mgravell @NickCraver

docs/ReleaseNotes.md

@@ -10,6 +10,7 @@ Current package versions:
 
 - Fix [#2426](https://github.com/StackExchange/StackExchange.Redis/issues/2426): Don't restrict multi-slot operations on Envoy proxy; let the proxy decide ([#2428 by mgravell](https://github.com/StackExchange/StackExchange.Redis/pull/2428))
 - Add: Support for `User`/`Password` in `DefaultOptionsProvider` to support token rotation scenarios ([#2445 by NickCraver](https://github.com/StackExchange/StackExchange.Redis/pull/2445))
+- Fix [#2449](https://github.com/StackExchange/StackExchange.Redis/issues/2449): Resolve AOT trim warnings in `TryGetAzureRoleInstanceIdNoThrow` ([#2451 by eerhardt](https://github.com/StackExchange/StackExchange.Redis/pull/2451))
 
 ## 2.6.104
 

src/StackExchange.Redis/ChannelMessageQueue.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Reflection;
-using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Channels;
 using System.Threading.Tasks;
@@ -126,6 +125,7 @@ public ValueTask<ChannelMessage> ReadAsync(CancellationToken cancellationToken =
         /// <param name="count">The (approximate) count of items in the Channel.</param>
         public bool TryGetCount(out int count)
         {
+#if NETCOREAPP3_1
             // get this using the reflection
             try
             {
@@ -137,6 +137,15 @@ public bool TryGetCount(out int count)
                 }
             }
             catch { }
+#else
+            var reader = _queue.Reader;
+            if (reader.CanCount)
+            {
+                count = reader.Count;
+                return true;
+            }
+#endif
+
             count = default;
             return false;
         }

src/StackExchange.Redis/Configuration/DefaultOptionsProvider.cs

@@ -225,31 +225,21 @@ protected virtual string GetDefaultClientName() =>
             string? roleInstanceId;
             try
             {
-                Assembly? asm = null;
-                foreach (var asmb in AppDomain.CurrentDomain.GetAssemblies())
-                {
-                    if (asmb.GetName()?.Name?.Equals("Microsoft.WindowsAzure.ServiceRuntime") == true)
-                    {
-                        asm = asmb;
-                        break;
-                    }
-                }
-                if (asm == null)
-                    return null;
-
-                var type = asm.GetType("Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment");
+                var roleEnvironmentType = Type.GetType("Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment, Microsoft.WindowsAzure.ServiceRuntime", throwOnError: false);
 
                 // https://msdn.microsoft.com/en-us/library/microsoft.windowsazure.serviceruntime.roleenvironment.isavailable.aspx
-                if (type?.GetProperty("IsAvailable") is not PropertyInfo isAvailableProp
+                if (roleEnvironmentType?.GetProperty("IsAvailable") is not PropertyInfo isAvailableProp
                     || isAvailableProp.GetValue(null, null) is not bool isAvailableVal
                     || !isAvailableVal)
                 {
                     return null;
                 }
 
-                var currentRoleInstanceProp = type.GetProperty("CurrentRoleInstance");
+                var currentRoleInstanceProp = roleEnvironmentType.GetProperty("CurrentRoleInstance");
                 var currentRoleInstanceId = currentRoleInstanceProp?.GetValue(null, null);
-                roleInstanceId = currentRoleInstanceId?.GetType().GetProperty("Id")?.GetValue(currentRoleInstanceId, null)?.ToString();
+
+                var roleInstanceType = Type.GetType("Microsoft.WindowsAzure.ServiceRuntime.RoleInstance, Microsoft.WindowsAzure.ServiceRuntime", throwOnError: false);
+                roleInstanceId = roleInstanceType?.GetProperty("Id")?.GetValue(currentRoleInstanceId, null)?.ToString();
 
                 if (roleInstanceId.IsNullOrEmpty())
                 {