Adding In-game Rendering mode switch.

[Dynacato]

I am suggesting an option to change render type in-game. Like, Forward+ to Mobile or Mobile to Compatibility and so.
Someone posted this proposal: godotengine#6423 and I think can be included with maybe some signals and runtime checks of which rendering mode you are to work.
Like:
RenderingDevice, type: enum
1 Forward
2 Mobile
3 Compatibility
4 Custom (just maybe)

To make things like:

   if Engine.RenderingDevice == 1:

      change_shadow_res(value)
      change_render_distance(value)
      forward_features(true)

  else:

       change_shadow_res(value)
       change_render_distance(value)
       forward_features(false)

I don't know if is possible inside the engine in the current state of the project but it would be a nice addition if is possible.