Entrypoint generation should always use fully qualified globalized type names

[Youssef1313]

See #4141 (comment)

Consider also using Embedded (not for the entrypoint type, but for the self registered extensions type)

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• ConfigurationBinder source generator encounters namespace conflicts in using statements dotnet/runtime#93498