Contributes to #4799

Now, there are 3 issues with ILinker:

1. For some reason it doesn't get rid of NpgsqlDataReader.GetValues (even though it's not called) (upd: it's called by DbEnumerator, which we return from GetEnumerator, Linker doesn't trim IEnumerable interface in console app even if it's not used dotnet/linker#3189)
2. NpgsqlDataReader.GetFieldValue is never called with T as object, yet ReadAsObject (which is only called with T as object) is never removed
3. Sometimes (RecordHandler.Read) ILinked doesn't realise that RuntimeFeature.IsDynamicCodeSupported makes sure nothing below is called with AOT, yet it's still preserved.

Probably a good idea to also check with .NET 8 (I've compiled on windows with .NET 7.0.1).
Same thing with .NET 8.

cc @roji @MichalStrehovsky