Trigger zoom from pan gestures when pressing ctrl

[aitorciki]

Fixes #72609

After the gestures refactor in #71685, zooming with ctrl + trackpad panning in macOS stopped working (4.0 beta16).

This PR aims at recovering that behavior, and extending it to other UI elements exposing zoom callbacks (pre-beta16, only CanvasItemEditor had this functionality hardcoded).

Panning up or right zooms in, down or left zooms out.

Zoom speed is tricky, as there is no factor in InputEventPanGesture we can leverage, and I haven’t found a way to consistently calculate one from deltas. I’ve decided to mimic the delta to factor logic in platform/macos/godot_content_view.mm, multiplying the default scroll zoom factor increase ratio by 0.3. Seems to work well for some UI elements (e.g. tilemaps), but is still too fast for others (e.g. animation tracks).

To keep things simple and avoid breaking existing user expectations, I’m not honoring the scroll pans/zooms toggle. I think it makes sense for panning to… pan by default (if this is deemed as potentially confusing to users who expect pan to behave like scroll, it’s an easy fix though).

EDIT: slightly reduced zoom speed, still feels good and natural in the canvas editor, and makes it a bit more precise in animation track editor.

[aitorciki]

Changes applied as per @AThousandShips comments.

[bruvzg]

It works on macOS (should be tested on Android as well, since pan gesture support is not macOS specific).

But I'm not sure why it's necessary, what's the point of using Ctrl+Pan instead of Zoom gesture?

[Riteo]

While we're at it I tested this on the WIP Wayland backend, which implements pan/zoom gestures. It works great! Too bad that this speed isn't really controllable but it looks like a bigger, more general, issue.

@bruvzg I actually see some value in this. I can see some people having issues with pinching reliably and honestly I kinda prefer this way of zooming as it's easier on the hand.

Still, considering that this is an already existing behavior I don't think that this is proposal material, so I approve :)

(Note that this hasn't still been tested on Android)

[aitorciki]

As @Riteo says, the pinch to zoom gesture is less precise than scrolling (specially for smaller steps) and for many folks not very ergonomic.
Also, scroll to zoom in pinch-supporting trackpads was lost in 4.0 beta 16 during a refactor, but had been available until then, this PR aims at recovering that existing functionality rather than adding new one (to @Riteo's point, configurable speed would be a great addition, but the current focus is in recovering the lost functionality).

[m4gr3d]

Tested on Android and it works well!

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.2.2.