feat(ui): expose a method for checking whether a message contains only emojis and should be boosted (use a bigger font size)

[stefanceriu]

• supports only text room message types
• enumerates through their body's grapheme clusters and check that every single one of them is an emoji
• part of the LazyTimelineItemProvider so that it can be opt in

[codecov]

Codecov Report

Attention: Patch coverage is 56.25000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 85.39%. Comparing base (4c4dd03) to head (08bfe16).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
...rates/matrix-sdk-ui/src/timeline/event_item/mod.rs	56.25%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4577      +/-   ##
==========================================
- Coverage   85.42%   85.39%   -0.03%     
==========================================
  Files         286      286              
  Lines       32213    32229      +16     
==========================================
+ Hits        27517    27522       +5     
- Misses       4696     4707      +11     

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[Hywan]

Neat!

[Hywan]

Well, it looks really good to me. Thanks! Can you rebase all your commits into a single one please?