Generally support input event for trackpad with multi-touch gestures

[Creta5164]

Describe the project you are working on

2.5D action platformer adventure.
But rather then this for context, I uses Godot between desktop and laptop frequently.

Describe the problem or limitation you are having in your project

May related proposal and PR

• Add touchscreen/trackpad event navigation in the 3D editor #2295
• Add InputEventRotateGesture for mac trackpads godot#101855
• Implement InputEventGesture (incl. Pan and Magnify) for all platforms godot#13139

So far as I know that Godot seems cannot handle trackpad multi-touch gestures input properly, and because of this, there's some proposals and PR about this.

When I see these PR and proposals, most of them are some feature specific (like 3D control improvement) or focused platform-specific environment like Mac book, but I think this should take into general approach for usability.

Trackpad that uses multi-touch gesture is more common nowdays, like most of Mac book, Magic trackpad and recent Windows based middle/high end laptops (including Surface products).

So I would suggest to support input event for trackpad with multi-touch gesture support.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

I would suggest to take a look PR that I reffered to, this can explain enough well after this proposal implemented.
godotengine/godot#101855
Except this proposal takes for general way.

So basically, add input event that can provide trackpad's multi-touch gesture data.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

See above PR's description.

If this enhancement will not be used often, can it be worked around with a few lines of script?

I don't think this can be able workaround because most of recent trackpad that uses multi-touch gestures has complicated conditions to handle these inputs.

For example, in Windows, you can move cursor with one finger slide, drag navigation with two finger slide, show/hide desktop or change focus window with three fingers slide.

Trying workaround these probably brings huge boilerplate codes in current state of Godot.

Is there a reason why this should be core and not an add-on in the asset library?

It appears common user use cases with hardware, so I think when implementing this proposal would brings many UX improvements potential afterward for trackpad users in both Godot editor itself and generic softwares that made with Godot.

And honestly, I don't want to navigate around pinch in-out trackpad repeatly in 2D view and GraphEdit node based interfaces...

* Written in mobile and partally used machine translator, expect typos.