Rich text: resolve owned event listeners once instead of per subscriber

[ellatrix]

What?

Rewrites subscribeOwnedListener so it resolves which element owns an event once per event, instead of every subscriber checking whether it owns the event on every event.

Alternative to #80517 (same fix, simpler dispatch).

Why?

Typing performance regression from editableRoot (#79105). Each editable subscribes owned listeners bound to the document, so all of them run on every event and each calls ownsSelection. With ~8 keydown subscriptions per editable and an editable per block, a keystroke in a 1250-block post is ~10,000 ownsSelection calls.

Note: this is what actually moves the metric. #80549 (avoid the forced layout) and #80548 (reorder the checks) both flatlined in CI — the cost is the number of calls, not the per-call work.

How?

One delegated listener per document, event type and phase. Its callback finds the owning element and fires its callbacks:

• These are editing and selection events, so the owner is the element that owns the selection (ownsSelection), and it contains the selection anchor.
• So the callback walks up from the selection anchor, testing ownsSelection, instead of testing every subscriber. That is O(DOM depth), not O(blocks). When there is no selection, an editable can still be focused, so it starts from the focused element instead.

selectionchange and ensureSelectionSync move onto subscribeOwnedListener too, so they ride the same per-element dispatch and stay ordered ahead of the element's other owned listeners, keeping the record synced before they run. This is required: without it, a later block's sync runs after the shared dispatch and input acts on a stale record.

Testing Instructions

1. Typing, splitting and merging, formatting, and cross-block navigation behave as before.
2. e2e passing locally: writing-flow (208), splitting-merging (44), rich-text, editable-root-compat (6).
3. Watch the type metric on codevitals for the drop.

Use of AI Tools

Written with the help of Claude Code.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

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

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Size Change: +68 B (0%)

Total Size: 7.75 MB

📦 View Changed

Filename	Size	Change
build/scripts/block-editor/index.min.js	428 kB	-64 B (-0.01%)
build/scripts/components/index.min.js	273 kB	-28 B (-0.01%)
build/scripts/rich-text/index.min.js	15 kB	+160 B (+1.08%)

_{compressed-size-action}