Repro

1. Install v6.0.100-alpha.1.21062.9 of the SDK from dotnet/installer.
2. Create a new blazorwasm project: dotnet new blazorwasm
3. Publish the project with trimming: dotnet publish -c Release (optionally dump the dependencies with /p:_TrimmerDumpDependencies=true
4. Examine the Microsoft.Extensions.DependencyInjection.ServiceCollectionContainerBuilderExtensions.BuildServiceProvider method in Microsoft.Extensions.DependencyInjection.dll
5. See that the call to RuntimeFeature.IsDynamicCodeCompiled still exists as does the path that invokes new DynamicServiceProviderEngine(services)

Expected behavior

RuntimeFeature.IsDynamicCodeCompiled should be false (it is in the S.P.Corelib assembly) and the code path handling DynamicServiceProviderEngine should have been trimmed.

Actual Behavior

It is not trimmed which is causing System.Reflection.Emit to not be trimmed.