Fixing the GetInterfaceMap tests for mono in the runtime repo. (#52566)

Fixing the GetInterfaceMap tests for mono in the runtime repo. (#52566)

Addressing 4 issues for GetInterfaceMap and default interface methods
 - Only methods marked as virtual on on interface should be added to the
   interface map. (no static or instance)
 - If the found target method is ambiguous (a diamond) the target is
   null.
 - If the found target method's class in an interface, then the target
   class is the interface class, else it is the class of the RuntimeType
   (aka this)
 - If the found target method is abstract (reabstraction) then the
   target is null.

Fixes #34389