Suggest mode 3/7: block-level capture (attribute and structural)

[adamsilverstein]

Part of #73411

What's in this PR

Adds the store-level interceptor that catches block mutations dispatched
straight to the block-editor store (the block-switcher variation picker,
programmatic writes), routing attribute drift into the overlay and reverting
the live block; captures structural edits (insert/remove/move) by tagging
the live block with a metadata.suggestion marker and recording the op; and
the overlay HOC that renders the pending-suggestion visual treatment (the
green attribute bracket and the strikethrough/dim/move-ghost overlays). The
revert guard and undo guard keep the interceptor's own writes off the undo
stack and out of its own subscribe loop, and the server hides un-accepted
structural insertions at render time. Inline text and formatting markers
are layered on top of this HOC in a later step.

Screenshot

Structural suggestions keep the block on the canvas and tag it instead of applying the change. A suggested move lands the block at its proposed position and leaves a ghost at the origin; a suggested removal keeps the block with a struck-through treatment:

Testing

This is one layer of the stack. To exercise the whole feature, #78994 bundles all seven layers into one branch and builds it in Playground:

👉 https://playground.wordpress.net/gutenberg.html?pr=78994

Enable Gutenberg > Experiments > Collaboration > Suggestion Mode, then follow the walkthrough in #73411, which also explains how to review the stack layer by layer.

---

Suggest mode stack

This rebuilds the manually-stacked Suggest mode work (#73411) as a GitHub Stack of 7 small, independently reviewable PRs, each building on the one below it:

1. #80427 - editor intent (edit/suggest/view) + experiment gate
2. #80428 - suggestion storage, REST controller, provider
3. #80429 - block-level capture (attribute + structural)
4. #80430 - inline marker primitive
5. #80431 - inline suggestion operations
6. #80432 - review UI (Apply/Reject sidebar + summary)
7. #80433 - inline live wiring, docs, e2e

The whole feature can be exercised end-to-end via the combined testing branch #78994 (Playground). Behind the "Suggestion Mode" experiment (Gutenberg > Experiments).

[github-actions]

Size Change: +7.13 kB (+0.09%)

Total Size: 7.83 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	519 kB	+5.23 kB (+1.02%)
build/styles/block-editor/content-rtl.css	6.15 kB	+488 B (+8.62%)	🔍
build/styles/block-editor/content-rtl.min.css	4.6 kB	+463 B (+11.18%)	⚠️
build/styles/block-editor/content.css	6.15 kB	+488 B (+8.62%)	🔍
build/styles/block-editor/content.min.css	4.6 kB	+466 B (+11.27%)	⚠️

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[github-actions]

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

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[github-actions]

Flaky tests detected in 70488b5.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/31052225217
📝 Reported issues:

• [Flaky Test] should insert media, convert to blocks, and undo in one step #36123 in /test/e2e/specs/editor/blocks/classic.spec.js