Fix virtual keyboard in the pointer demo

[AtomicAntt]

Simple change to address #792 where we get the Viewport outside of the SubViewport containing the UI and push input there instead of using:

Input.parse_input_event(input)

This fixes the virtual keyboard in the demo, as the demo has a SubViewport when implementing the spectator view which seems to block the input event?

One thing to note is that after this change, I still can't edit the lines in the pointer demo with my desktop keyboard, but the virtual keyboard will work.

Works on Godot 4.4.1 and 4.6.2 in the demo, and on another separate Godot XR project (without spectator view).

[BastiaanOlij]

Hmmm, this makes a lot of sense. I do think this should probably become get_tree().get_root() so input is always sent to the root viewport and propagated upwards.

Sorry for the late response btw, I've been focusing on XRT2. Need to find some time to properly test this and see if we're not missing anything else but this is definately a fix that should be part of the next release.