Rewrite Gui in 3D demo to use Physics Picking for mouse events

[Sauermann]

Rework Gui in 3D Demo to handle mouse events via Physics Picking instead of in _unhandled_input.

This brings several benefits:

• Correctly handle cases, where the 3D-GUI is located behind other collision objects. (currently one can interact with it, even when there is a collision object (e.g. wall) between camera and the 3D-GUI)
• Proper passive hovering support

This allows also to make simplifications in the code, because 3D-mouse position no longer needs to be calculated manually.

This PR does for 3D, what godotengine/godot#58334 did for 2D-SubViewportContainer.

Needs to work correctly godotengine/godot#78383 (included in V4.2)

Updated 2023-08-31: Make sure to include Velocity in InputEventMouseMotion when sending event to SubViewport. (Necessary for solving #925 (comment))
Updated 2023-11-10: Ordering of lines in config files has changed.
Updated 2024-02-21: Rebase after #1013

[akien-mga]

For the record, your commit seems not to be linked to your GitHub account. See: Why are my commits linked to the wrong user? for more info.

[Sauermann]

@akien-mga thanks, first commit to a repository and I missed to set it up.

[Calinou]

Tested locally with 4.2.dev godotengine/godot@6758a7f8c (Linux), it mostly works as expected. One issue with OptionButtons is that their popup doesn't update when you don't move the mouse but the camera moves:

simplescreenrecorder-2023-08-24_01.00.21.mp4

[Sauermann]

their popup doesn't update when you don't move the mouse but the camera moves

My current understanding is, that this needs to be resolved in the main-repository, since I can't do anything from this side to fix this. It is however not a regression, because the current implementation also has this problem.

[Calinou]

Note: Do not merge until 4.2 is released, as the master branch should keep working with 4.1.x until 4.2.stable is released. Marking as draft accordingly to avoid accidental merge.

[Sauermann]

One issue with OptionButtons is that their popup doesn't update when you don't move the mouse but the camera moves

I found a solution for this problem: godotengine/godot#81243

[fire]

Is everyone ok with the merge of Rewrite Gui in 3D demo to use Physics Picking for mouse events?

[Calinou]

Tested locally on 4.2.1, it works as expected.