regression: federated reactions dropped or sent as raw shortcode text

[KevLehman]

Proposed changes (including videos or screenshots)

The federation emoji converter (ee/packages/federation-matrix/src/utils/emojiConverter.ts) built its shortcode maps from the emojibase preset, while the app emoji list is joypixels-first since the native emoji migration (#39411, aligned by #41587). The converter was never updated, breaking federated reactions in both directions:

• RC → Matrix: joypixels-only shortnames (:slight_smile:, :upside_down:, tone variants like :hand_splayed_tone3:) don't resolve, so Matrix/Element users see the literal shortcode text as the reaction key instead of the emoji.
• Matrix → RC: unicodeToShortname emits emojibase-primary names (:grinning_face_with_big_eyes:) that are not in the app's emoji.list, so setReaction throws Invalid emoji provided and the reaction is silently dropped. Affects ~620 emojis including 😃 😄 😅 😘 🤗 😎.
• Matrix → RC (unqualified keys): reaction keys without VS16 (bare 👍, ❤ — what most clients send) missed the map keyed on fully-qualified strings and were dropped the same way.
• Same-emoji reactions split into two chips (:thumbsup: local vs :+1: federated), and contested shortcodes diverged in meaning (:cat: → 🐈 outbound while RC renders 🐱).

Fix aligns the converter with the app's emoji data:

• joypixels-first shortcode lookup (same pattern as regression: shortcodes changed meaning #41587)
• bare-form (VS16-stripped) unicode aliases for inbound keys
• legacy emojione shortcode backfill (mirrors the app's legacyEmojioneMap)

Issue(s)

Regression from #39411

Steps to test or reproduce

1. Federate a room between Rocket.Chat and a Matrix server (Element).
2. From RC, react to a message with 🙂 (:slight_smile:) → Element previously showed the literal text :slight_smile:; now shows 🙂.
3. From Element, react with 😃 or bare 👍 → RC previously dropped the reaction with Invalid emoji provided in logs; now the reaction appears and aggregates with local :thumbsup: reactions.

Further comments

Unit spec added covering both directions, tone variants, legacy shortcodes and unqualified keys. No changeset (regression fix targeting release-8.7.0).

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.40%. Comparing base (9bd5a7d) to head (3e42984).
⚠️ Report is 1 commits behind head on release-8.7.0.

Additional details and impacted files

@@              Coverage Diff               @@
##           release-8.7.0   #41606   +/-   ##
==============================================
  Coverage          68.40%   68.40%           
==============================================
  Files               4139     4140    +1     
  Lines             158309   158335   +26     
  Branches           28305    28324   +19     
==============================================
+ Hits              108290   108314   +24     
- Misses             44882    44884    +2     
  Partials            5137     5137           

Flag	Coverage Δ
e2e	58.85% <ø> (-0.03%)	⬇️
e2e-api	45.35% <ø> (-0.02%)	⬇️
unit	70.35% <100.00%> (+0.02%)	⬆️

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