Implement MOUSE_MODE_CAPTURED for iOS

[celyk]

Tested versions

v4.2.1.stable.official [b09f793]

System information

iPadOS 17.4, iPad 9th gen

Issue description

I'm trying to use a bluetooth mouse on my iPad to control an FPS camera. To do this, the mouse should be locked into the center of the screen and hidden. I tried MOUSE_MODE_CAPTURED but it has no affect. It is not implemented.

Keyboard and mouse gaming is possible to do on iPad today. For instance, I can play FPS games through Steam link just fine. See this talk by Apple. It has a mouse locking example at 7:30
https://developer.apple.com/videos/play/wwdc2020/10617

Steps to reproduce

Minimal script for enabling mouse lock/capture

extends Node

func _ready():
	DisplayServer.mouse_set_mode(DisplayServer.MOUSE_MODE_CAPTURED)

Minimal reproduction project (MRP)

mouse-capture-MRP.zip

[bruvzg]

Currently, we are using only touch input (mouse events are emulated), but on recent iOS versions it should be possible to read raw mouse input directly. I'm not sure about MOUSE_MODE_CAPTURED and hiding cursor. Seems to be possible as well.