Cleanup of c# api files and bindings generator

- We no longer generate RID and NodePath C# classes. Both will be maintained manually.
- We no longer generate C# declarations and runtime registration of internal calls for the following classes: RID, NodePath, String, GD, SignalAwaiter and Godot.Object (partial base).
- We no longer auto-generate the base members of Godot.Object. They will be maintained manually as a partial class.

This makes it easier to maintain these C# classes and their internal calls, as well as the bindings generator which no longer generates C# classes that don't derive from Godot Object, and it no longer generates the Godot.Object base members (which where unreadable in the bindings generator code).

- Added missing 'RID(Object from)' constructor to the RID C# class.
- Replaced MONO_GLUE_DISABLED constant macro with MONO_GLUE_ENABLED.
- Add sources in module/mono/glue even if glue is disabled, but surround glue files with ifdef MONO_GLUE_ENABLED.

modules/mono/SCsub

@@ -57,6 +57,7 @@ def make_cs_files_header(src, dst):
 
 
 env_mono.add_source_files(env.modules_sources, '*.cpp')
+env_mono.add_source_files(env.modules_sources, 'glue/*.cpp')
 env_mono.add_source_files(env.modules_sources, 'mono_gd/*.cpp')
 env_mono.add_source_files(env.modules_sources, 'utils/*.cpp')
 
@@ -72,9 +73,7 @@ vars.Update(env_mono)
 
 # Glue sources
 if env_mono['mono_glue']:
-    env_mono.add_source_files(env.modules_sources, 'glue/*.cpp')
-else:
-    env_mono.Append(CPPDEFINES=['MONO_GLUE_DISABLED'])
+    env_mono.Append(CPPDEFINES=['MONO_GLUE_ENABLED'])
 
 if ARGUMENTS.get('yolo_copy', False):
     env_mono.Append(CPPDEFINES=['YOLO_COPY'])