[AOT] Improve Results<...>.PopulateMetadata implementation

[JamesNK]

There currently isn't a good way to call static generic methods from reflection. Results<...>.PopulateMetadata currently requires DAM methods and some non-ideal reflection.

Some options are described here: #46082 (comment)

[JamesNK]

Improve compiler: dotnet/runtime#81204
Improve C#: dotnet/csharplang#6308