[corlib] Improve reflection interface definitions (#16324)
* [corlib] Fix _Type interface definition.
* [corlib] Fix Type class attributes.
* [corlib] Fix _MethodInfo interface definition.
* [corlib] Fix MethodInfo class attributes.
* [corlib] Merge MethodInfo partial definitions.
* [corlib] Remove leftovers from testing.
* [corlib] Do not define new attributes for MOBILE build.
* Bump API snapshot submodule
* [corlib] Add explicit _MethodInfo.GetType() implementation.
* Bump API snapshot submodule
* [csproj] Update project files