Editor: Add a filter for the emoji a note can be reacted with

[adamsilverstein]

Backport of the reaction emoji filter from WordPress/gutenberg#84200 - this one is stacked on #10930 and should be reviewed after it, the first commits here are from that PR.

Claude did the port from the Gutenberg side; here is the rundown:

Adds a wp_note_reaction_emojis filter so a site can add or remove the emoji a note can be reacted with, or turn adding reactions off with an empty list.

• Adds wp_get_note_reaction_emojis(), which runs the filter and drops malformed entries, empty labels and duplicate keys, and wp_get_note_reaction_keys().
• Adds wp_normalize_note_reaction_key(), which normalizes filtered keys to the stored form (lowercase, padded to four digits, U+FE0F dropped) and rejects surrogates and values past U+10FFFF.
• The comments controller validates reactions against wp_get_note_reaction_keys(), replacing its private hardcoded list.
• get_block_editor_settings() passes the list to the editor as noteReactionEmojis, so the reaction menu offers the same emoji the REST API accepts.

Existing reactions whose emoji is filtered out stay visible and can still be removed by their authors.

Only the commits after backport-note-reactions-meta-70 belong to this change: adamsilverstein/wordpress-develop@backport-note-reactions-meta-70...backport-note-reaction-emoji-filter

Trac ticket: https://core.trac.wordpress.org/ticket/66276

Test plan

• Add a filter that drops the heart and adds a unicorn:

  add_filter( 'wp_note_reaction_emojis', function ( $emojis ) {
  	$emojis   = array_slice( $emojis, 1 );
  	$emojis[] = array( 'hexKey' => '1f984', 'label' => 'unicorn' );
  	return $emojis;
  } );

• POST a 1f984 reaction to a note: 201. POST 2764: 400 rest_comment_invalid_reaction.
• Return an empty array from the filter, then DELETE an existing reaction of your own: 200.
• Check that noteReactionEmojis in the editor settings matches the filtered list.
• phpunit --group comment,notes,restapi and phpunit --filter Tests_Blocks_Editor

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5.5
Used for: Porting the code and tests from the Gutenberg PR and writing this description. I will review and test.

🤖 Generated with Claude Code

https://claude.ai/code/session_017FGp5zYv14MKoTuh3RFuWi

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[github-actions]

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