Autocompleters: Don't pre-encode mention search terms

[Mamaduka]

What?

See #77185 (comment).

PR fixes the user mention autocompleter (@) to return correct results for non-Latin search terms - Georgian, Japanese, Cyrillic and emoji.

Why?

Both mentions of completers passed search: encodeURIComponent( filterValue ) to getUsers. addQueryArgs already encodes query values, so the term was double-encoded and the server received the literal text %E1%83%90%E1%83%91.

WordPress runs the REST search arg through sanitize_text_field(), which strips every percent-encoded sequence. Latin letters aren't encoded, so they survive, and the bug stays hidden. Non-Latin characters are encoded in full and get erased:

typed	server receives	after sanitize_text_field
abc	abc	abc
აბგ	%E1%83%90%E1%83%91%E1%83%92	""

An empty search matches everything, so @აბგ listed every user on the site.

The encoding was correct when the completer built its own query string ('?search=' + encodeURIComponent( search )), but became a double-encode when #33028 moved it to getUsers.

How?

Pass filterValue through unencoded and let addQueryArgs encode it, matching the existing links completer. Same one-line fix in the post and Notes mentions completers.

Testing Instructions

1. Create a user with a non-Latin display name, e.g. გიორგი მამადაშვილი.
2. In a paragraph, type @გიორგი.
3. Only that user is suggested. On the trunk, every user on the site is suggested.

Covered by a new e2e test in autocomplete-and-mentions.spec.js, which fails on trunk.

Use of AI Tools

Assisted by Claude.

[github-actions]

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Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: noruzzamans <noruzzaman@git.wordpress.org>

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[github-actions]

Size Change: -17 B (0%)

Total Size: 7.73 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	499 kB	-17 B (0%)

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[noruzzamans]

Tested and confirmed the fix works as expected.
Before:

After:

[t-hamano]

LGTM! It works correctly with both emojis and Japanese.

mention-search.mp4

[Mamaduka]

Thanks for testing. Labeling this for backport, since mentions is a new feature for the notes.

[github-actions]

I just cherry-picked this PR to the wp/7.1 branch to get it included in the next release: 2a8a6b9

[adamsilverstein]

🎉 Excellent work @Mamaduka - thanks!

[t-hamano]

I just cherry-picked this PR to the release/23.6 branch to get it included in the next release: 6f920b5