Block Editor: Locate widget form inside post-editor iframe + clone iris/color-picker deps

[Misplon]

Summary

• Fixes the real bug: SOWB widget forms (Features Widget repeater, settings sections, color pickers) wouldn't open in the WP 6.5+ post editor because the post editor renders blocks inside <iframe name="editor-canvas">, but sowbGetBlockForm() only knew about the Site Editor canvas selector. Form lookup returned empty, $mainForm.sowSetupForm() was never called, and no click handlers were ever bound.
• Robustness extras: Adds #jquery-touch-punch-js, #iris-js, and #wp-color-picker-js to the iframe-clone allowlist so the asset chain is complete. Verified via in-page diagnostic that these were already present via WP's bridge — but having them in the explicit allowlist closes a real gap and is the same shape as existing entries.

Root cause (verified with runtime diagnostic, not guessed)

Inline debug emitted into both contexts on WP 6.9.4 confirmed:

• IFRAME (name=editor-canvas): [data-block] and .siteorigin-widget-form-main exist; data(sow-form-setup)=undefined; all jQuery / jQuery UI / wp-color-picker globals already present.
• PARENT: [data-block] count is 0 — block tree lives only in the iframe.
• sowbGetBlockForm() queried the parent doc, found nothing, and the form-init bailed out.

The fix re-resolves the editor canvas on every call (Site Editor selector → post editor iframe selector → parent-doc fallback) and uses .contents() to descend into whichever iframe is mounted. Caching is preserved but only written when the canvas is actually present, so we never lock in an empty result before the iframe mounts.

Test plan

• WP 6.9.4 post editor: Features Widget repeater item header expands on click.
• WP 6.9.4 post editor: settings section header expands on click.
• WP 6.9.4 post editor: drag-to-reorder works on repeater handles.
• WP 6.9.4 post editor: color-picker fields render with alpha slider.
• WP 7.0 post editor: same four checks.
• WP 7.0 Site Editor: same four checks (Site Editor branch is unchanged in shape).
• widgets.php Block Widgets screen (no iframe): widget forms still open and behave (parent-doc fallback branch).
• No new console errors related to [data-block] or jQuery scope.

[Misplon]

Superseded by #2308, which opens against a fresh branch off develop with four atomic commits in plan order. The previous branch had a wall-knock revert pair from a misdirected fix attempt; the diagnostic-confirmed work has been restated cleanly in #2308.