Add testing for ASP.NET Core Identity model

[ajcvickers]

Fixes #11838

The intention here is not to test ASP.NET Core Identity. It is instead to test that:

• The Identity model continues to build correctly with new versions of EF Core and across multipler providers, including external providers once they adopt these tests
• The queries issues by Identity continue to work in new versions and across providers
• The common (documented) customizations of the Identity model continue to work

[smitpatel]

Can you

• Add assembly level condition for Sqlserver test suit https://github.com/dotnet/efcore/blob/main/test/EFCore.SqlServer.FunctionalTests/Properties/TestAssemblyConditions.cs
• Update EFCore.Relational.slnf/EFCore.slnf
• Add SqlServer specific proj here

  efcore/eng/helix.proj

  Line 17 in 2abab27

  <SqlServerTests>$(RepoRoot)/test/EFCore.SqlServer.FunctionalTests/*.csproj;$(RepoRoot)/test/EFCore.OData.FunctionalTests/*.csproj</SqlServerTests>

• Remove specs project here

  efcore/eng/helix.proj

  Line 32 in 2abab27

  <XUnitProject Remove="$(RepoRoot)/test/EFCore.Relational.Specification.Tests/*.csproj"/>

[ajcvickers]

@smitpatel Done. (Hope I got it all right!)

[smitpatel]

Specs test generally don't depend on relational. But identity model would be hard to use with non-relational database (except for inmemory), so may be it is fine to leave this as is. There is also an option to add in the name that this is relational specific, like our relational.specs tests. I don't mind either way.

[ajcvickers]

This was what I discussed a couple of weeks ago in triage. ASP.NET Identity references the relational package, so even if you use Identity with a non-relational provider (like in-memory) there is still a reference to Relational brought in transitively. The idea here is to make sure we reference our build of Relational, and not just happen to use the one from Identity.