Implement OS agnostic InputEventGesture with Pan, Pinch, and Twist

[jeremyz]

this is shamelessy inspired by Federico-Ciuffardi's job on #36953

implementation of thresholds to limit the amount of
emitted events will come later.

this is related to #13139 (and #37754 for 3.2 branch)

Bugsquad edit: Fixes #13139.

[jeremyz]

This has been tested on X11 and android on 3.2 branch, see #37754 (test scene included).

[akien-mga]

Sorry for the delay reviewing this, and thanks for keeping at it! It's looking good and I agree that such an OS agnostic approach is the best to support these events on all platforms that support touch input.

BTW, what does it imply for the current only platform-specific implementation for macOS?

Would be good to have some review/feedback from @godotengine/input @RandomShaper, maybe also potential users of the feature like @HEAVYPOLY?

[jeremyz]

No worries about the delay, there's a lot of PR, you do what you can.
BTW, good PR review, you've nailed all my mistakes ! they should be fixed now.
About the native Gesture events, (Android/OSX) I'm processing the issue right now, because yes, there is one.
I don't have OSX hardware to test, if someone has some valuable input I'll appreciate it.
I'm on it, will come back with something this week-end.

[madmiraal]

I'm not convinced this is the right way forward.

I agree that we should detect gestures in the Godot input system instead of in each individual platform i.e. this PR is better than #36953. And I agree that gestures should be named after their action not how they’re interpreted i.e. "Pinch" is better than "Magnify". However, I'm not convinced these are the gestures that we should be implementing. My concerns include, but are not limited to:

• Why does “Pan” (which is an interpretation not an action) require two fingers? Why not just use InputEventScreenDrag as a single finger gesture (since all drags require a touch). It already includes a relative and a velocity parameter?
• Why include “Twist” (which is also an interpretation not an action). Why not simply include the change in angle between the two fingers as another parameter of “Pinch”?

At the very least, I think there should be an agreed proposal to support which gestures, if any, we should implement.

[madmiraal]

I've created godotengine/godot-proposals#4340 to facilitate the discussion.

[stevenctl]

I think you're spot on in your opinion about naming, but at the same time these are supported on mac and work great. I don't see why that should block allowing that on other platforms.