* Don't manipulate selection in any way. Leave that to Godot, and I'll fix issues in the engine if needed.
* Unify speech rendering of tree rows. This results in more useful announcements of buttons and such when tree items receive focus.
* Only handle `ui_up` and `ui_down` to ensure that focus won't leave a tree when the top-most or bottom-most row is arrowed past.
* Add a bit of handling to strip out duplicate collapse/focus events generated by the remote `SceneTree` in an active game.
UI controls occasionally trap focus and make navigation impossible. Now, Ctrl+escape toggles a mode that attempts to intercept and generate UI focus events and bypass the control's own handling. This can probably be refined, but for now it allows escaping of `TextEdit` via tab. It also won't work everywhere--inn particular, arrowing around still traps focus in trees. But it is at least possible to tab out of most traps.
Further, event generation was cleaned up some. We specifically need to generate `KeyEvents` under Android because, IIRC, it wasn't enough to simply create and send some types of events. We now have two distinct generation strategies. These can probably be combined and streamlined, but for now this works.
`Accessible` is now a child of its `Control`. This helps to ensure that everything gets cleaned up as it should. Further, node additions no longer scrape the entire scene.
This may introduce regressions and has only been lightly tested, but without it, `ScreenReader` leaked in various circumstances, including some that caused segfaults on exit.
On one hand, it's a bit confusing that UIs can be arrowed around independently of tab/shift-tab. Arrow navigation doesn't feel as intuitive, as it isn't obvious where you'll land.
On the other, it's quicker to navigate between areas of the editor UI by arrowing up/down between controls, and may solve the issue of having to tab a million times to traverse all controls. This also allows for in-game UIs to be traversed using arrows and, quite probably, gamepads as well.
