[Bug]: Avoid explicitly casting the result of GetService/GetServiceAsync, use the extension methods instead

[kartheekp-ms]

NuGet Product Used

Visual Studio Package Management UI, Visual Studio Package Manager Console

Product Version

VS

Worked before?

No response

Impact

No response

Repro Steps & Context

Address https://github.com/NuGet/NuGet.Client/pull/4324/files#r737866598 comment.

Verbose Logs

No response

[nkolev92]

Weird, that API has slipped through the APi banning I added in NuGet/NuGet.Client@927e225.

https://github.com/NuGet/NuGet.Client/blob/dev/build/BannedSymbols.txt#L17

AsyncPackage seems to explicitly declare that method too, which means there is no extension method we can use directly.

Given that AsyncPackage impls the service provider, we should make sure we're calling it on the interface.

[nkolev92]

We should ofc ban the AsyncPackage version of GetServiceAsync.