[libraries][iOS][tvOS] Fix case of assembly in ActivatorTests

[mdh1418]

Part of #52072
Part of #34030

TestingCreateInstanceFromObjectHandleFullSignature and TestingCreateInstanceFromObjectHandle fail on iOS and tvOS with the following error

System.Tests.ActivatorTests.TestingCreateInstanceFromObjectHandleFullSignature(physicalFileName: \"TestLoadAssembly.dll\", assemblyFile: \"testloadassembly.dll\", type: \"publicclasssample\", ignoreCase: True, bindingAttr: Instance | Public, binder: DefaultBinder { }, args: [], culture: , activationAttributes: null, returnedFullNameType: \"PublicClassSample\")
    System.IO.FileNotFoundException : Could not load file or assembly '/Users/mdhwang/Library/Developer/CoreSimulator/Devices/71D00C72-A1BD-4EF7-87EA-B22842EC1650/data/Containers/Bundle/Application/81C73384-2A96-498B-B352-4F61452336F8/System.Runtime.Tests.app/testloadassembly.dll' or one of its dependencies.
       at System.Runtime.Loader.AssemblyLoadContext.InternalLoadFromPath(String assemblyPath, String nativeImagePath)
   at System.Runtime.Loader.AssemblyLoadContext.LoadFromAssemblyPath(String assemblyPath)
   at System.Reflection.Assembly.LoadFrom(String assemblyFile)
   at System.Activator.CreateInstanceFrom(String assemblyFile, String typeName, Boolean ignoreCase, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Tests.ActivatorTests.TestingCreateInstanceFromObjectHandleFullSignature(String physicalFileName, String assemblyFile, String type, Boolean ignoreCase, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, String returnedFullNameType)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

System.IO.FileNotFoundException is hit in https://docs.microsoft.com/en-us/dotnet/api/system.activator.createinstancefrom?view=net-5.0 as a result of the assembly file not found.
Looking at the memberdata, the test with TestLoadAssembly.dll works, whereas testloadassembly.dll leads to the wrong exception.
Looking at the expected throw, TypeLoadException requires that just the typename not be found within the assembly, so changing the case of the assembly file is not necessary.

This PR looks to modify the test data to remove the physicalFileName parameter and to have the correctly typed assembly file, and by doing so, the tests pass on iOS and tvOS.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[mdh1418]

It looks like #36896 and the rest of #34030 in AppDomainTests has a similar casing issue that had been partially resolved by #56586.
Ill have a follow up PR that will address the AppDomainTests separately and close #34030 there.