Fix missing ServiceCallSite.Key causing an unkeyed cache entry to be overwritten by a keyed instance

[IliaShuliatikov]

Fix missing ServiceCallSite.Key causing an unkeyed cache entry to be overwritten by a keyed instance when using DynamicServiceProviderEngine and cover all cases (Generic (TryCreateOpenGeneric) and Enumerable (TryCreateEnumerable) and the basic one (TryCreateExact) ) with unit tests.

Fixes #111795

[KalleOlaviNiemitalo]

I feel that ServiceProviderExtensionsTest might not be the best class to contain the new tests, because they are intended to test the service container itself rather than the extension methods.

[steveharter]

I feel that ServiceProviderExtensionsTest might not be the best class to contain the new tests, because they are intended to test the service container itself rather than the extension methods.

Perhaps the class CallSiteTests in file CallSiteTests.cs would be a better match?

[IliaShuliatikov]

@KalleOlaviNiemitalo, @steveharter, that's a good point, thanks.

I moved the new tests to the CallSiteTests class, made them more specific to ServiceCallSite and removed unnecessary dependency on DynamicServiceProviderEngine, please take a look.

[steveharter]

Thanks for fixing this.

[IliaShuliatikov]

Glad I could help and make .NET a bit better!