Adds a control-bar toggle (next to the Add Keyframe diamond) that, when off,
makes a manual drag/resize/rotate/panel edit on an already-keyframed element
shift the whole tween by the edit's delta instead of inserting or updating a
keyframe at the playhead. The animation's shape is preserved, just moved.
Wired into every path that can auto-record a keyframe:
- canvas drag-to-move (tryGsapDragIntercept, reuses the existing Alt-drag
"shift whole path" behavior)
- canvas resize/rotate (tryGsapResizeIntercept, tryGsapRotationIntercept)
- design-panel property edits (useAnimatedPropertyCommit)
- motion-path keyframe-node dragging (MotionPathOverlay), the path a plain
click-drag on a keyframed element's canvas shape actually takes, since the
element renders exactly at its current keyframe's position
The shared shift helper reuses synthesizeFlatTweenKeyframes for materializing
a flat tween instead of hand-rolling it, and lives in its own file
(gsapWholePropertyOffsetCommit.ts) to keep gsapDragCommit.ts under the
600-line cap, mirroring the existing gsapDragPositionCommit.ts split.
Fixes#1808
Vance Ingalls