Media Editor: auto zoom-out during freeform crop handle drag

[ramonjd]

Summary

• When dragging a freeform crop handle outward toward (or past) the image edge, the image now auto-scales down so the crop can keep growing past its original footprint.
• On release, the view settles back to a normal fit with the new crop centered and zoom >= 1 restored.
• Addresses the follow-up from Media Editor experiment: add experimental image editor and cropper #77479 (comment).

How it works

A transient isResizing flag gates a sub-unit-zoom regime in the cropper reducer:

• BEGIN_RESIZE on handle pointerdown relaxes the zoom >= 1 floor and pins base* fields.
• During drag, handleCropChange dispatches a combined SET_CROP_RECT + SET_ZOOM where zoom is computed so the growing crop fits the container with a small margin (RESIZE_FIT_MARGIN = 0.95).
• restrictPanZoom in containment skips the cover-floor bump while the flag is set — the camera math is linear and handles zoom < 1 without modification (verified by test + JSDoc in createCamera).
• END_RESIZE clears the flag; SETTLE_CROP then re-expands the crop, recenters, and enforceContainment restores the cover invariant. SETTLE_CROP also self-heals the flag so a caller that forgets END_RESIZE still lands in a coherent state.

Behavior is gated to freeform crops — fixed aspect-ratio presets are untouched.

Tests

• New focused suite core/test/sub-unit-zoom.ts covers the sub-unit regime: flag transitions, sub-unit zoom through SET_ZOOM and enforceContainment, settle self-heal, zoom-back-to-≥1, and camera round-trip at zoom=0.5.
• New integration test react/hooks/test/resize-zoom-out.ts exercises the full dispatch chain through the state hook.
• The 12k-assertion preview-export-parity.ts suite is deliberately untouched and still green — the sub-unit regime is transient and never escapes into committed state.

Test plan

• Drag the east/west/north/south handles outward on a 16:9 image — image scales down, handles keep tracking.
• Drag the nw/ne/sw/se corners outward — same behavior.
• Release — crop re-centers, zoom snaps to >= 1.
• Drag a handle inward — image stays put until release.
• With a fixed aspect ratio preset active — zoom-out does NOT engage; clamp behavior matches trunk.
• Rotate (15 degrees) + drag — still works.
• Flip + drag — still works.
• Existing 12k preview-export parity suite still passes.

Follow-ups (not in this PR)

• v4 smoother settle transition (width/height/left/top animation).
• Approach-driven zoom-out (start shrinking before the handle reaches the edge).
• createCamera -> getImageFit delegation refactor.

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Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>

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