Added documentation to some `add_*_plugin` methods
Added documentation to some `add_*_plugin` methods

Added documentation to some `add_*_plugin` methods and the corresponding `remove_*_plugin` methods.
Added an example of how to register a plugin to `add_inspector_plugin` and linked to it in the other methods.

(cherry picked from commit e849157e074fdc302be9e7f7a891bea53ed5cee3)

Proofread add_*_plugin/remove_*_plugin descriptions in EditorPlugin

(cherry picked from commit 21f09616102a6b45f6533c58da33a4f973468ae6)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot