RichTextLabel Forced focus_mode when selection_enabled is active

[Spartan322]

Godot version: Godot Mono 3.2 Beta 2

OS/device including version: Manjaro Arch Linux

Issue description: RichTextLabel is forced into acting like having a focus_mode of All regardless of focus_mode property when selection_enabled is set to true. If this is intended behavior, I'll be willing to submit an issue to the docs on the subject, as it should at least be documented.

Steps to reproduce:

1. Create a new project with a scene containing only a RichTextLabel
2. Set the RichTextLabel's focus_mode to None and selection_enabled to true
3. Play game and click on the RichTextLabel