Add Spine43 object and timeline sequencer support

Adds a Spine43Object extension with the Spine 4.3 runtime adapter, runtime object implementation, bundled pixi-spine browser runtime, and editor-facing metadata for animation, skin, slot, bone, transform, track, event, debug, and resource controls.

Adds a TimelineSequencer extension with runtime timeline registration, playback, seeking, pause/resume, looping, speed control, object target binding, marker/status conditions, and time/duration/progress/speed expressions. Includes runtime helpers for easing, interpolation, path evaluation, timeline management, and timeline playback tests.

Integrates both features into the GDevelop editor by adding Timeline project storage and a Timeline editor tab, exposing timeline items in the Project Manager, adding timeline-specific parameter fields, registering the new runtime files, and wiring editor containers, tab restoration, toolbars, scene/editor displays, object editors, and Chinese locale text.

Adds explicit Flow type boundaries for the new Spine 4.3 name fields, Timeline name fields, and Spine editor preview/inspector helpers so the official Linux CI type checks can validate the added editor code reliably.

Author: mousekkkss

Extensions/Spine/JsExtension.js

@@ -59,6 +59,7 @@ module.exports = {
       .addIncludeFile('Extensions/Spine/managers/pixi-spine-atlas-manager.js')
       .addIncludeFile('Extensions/Spine/managers/pixi-spine-manager.js')
       .setCategory('Advanced')
+      .setHidden()
       .setOpenFullEditorLabel(_('Edit animations'));
 
     object