Report precise locations for generics in analyzer

Warnings like `IL2091` about generic arguments not satisfying the requirements of annotated generic parameters could point to the specific argument that doesn't match, instead of the full generic name. I think the precise warning locations would be worth implementing since it gives a better UX, especially when there are multiple arguments that produce warnings for the same generic method.

Tracking as a possible future improvement to https://github.com/dotnet/linker/issues/2364.