Implement ResourceManager/ResourceMap to align with WinAppSdk

[nickrandolph]

With the new class library structure it's somewhat difficult to load resources in code.
Uno.Extensions provides a wrapper for this but without this accessing resources from the class library requires two branches of code, one for WinAppSdk that uses ResourceMap and one that uses and overloaded ResourceLoader constructor that takes the name of the class library.

The idea would be to provide an implementation of ResourceManager/ResourceMap in Uno that aligns with the WinAppSdk

Source issue: #11786