Fix size regression in DependencyInjection (#56843)

Fix size regression in DependencyInjection (#56843)

With the new 6.0 TFM, we are no longer checking IsDynamicCodeCompiled to fall back to Reflection on Blazor WASM. Thus we are now using IL Ref Emit on WASM.

The issue was the #ifs were no longer correct for the new TFM. I've made the #ifs consistent across DI and DI.Abstractions such that the #ifs are for old TFMs and any new TFM will use the #else block.

Fix #56779