feat: use graphemer instead of grapheme-splitter

[oceandrama]

PR Checklist

• Addresses an existing open issue: fixes Enhancement: use graphemer instead of grapheme-splitter #7068
• That issue was marked as accepting prs
• Steps in Contributing were taken

[typescript-eslint]

Thanks for the PR, @oceandrama!

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The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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✅ Successfully ran 25 targets

• Node 18 - nx test eslint-plugin
• Node 14 - nx test eslint-plugin --coverage=false
• Node 18 - nx test visitor-keys
• Node 18 - nx run-many --target=build --parallel --exclude website
• Node 18 - nx test utils
• Node 18 - nx test type-utils
• nx run-many --target=typecheck --parallel
• Node 14 - nx test typescript-estree --coverage=false
• Node 18 - nx test parser
• Node 14 - nx test scope-manager --coverage=false
• Node 14 - nx run-many --target=build --parallel --exclude website
• Node 18 - nx test typescript-estree
• Node 14 - nx test eslint-plugin-internal --coverage=false
• nx run-many --target=lint --parallel
• Node 14 - nx test visitor-keys --coverage=false
• nx run-many --target=build --parallel --exclude website
• Node 18 - nx test eslint-plugin-tslint
• Node 14 - nx test eslint-plugin-tslint --coverage=false
• Node 14 - nx test ast-spec --coverage=false
• Node 14 - nx test type-utils --coverage=false
• Node 14 - nx test parser --coverage=false
• Node 18 - nx test scope-manager
• Node 18 - nx test eslint-plugin-internal
• Node 18 - nx test ast-spec
• Node 14 - nx test utils --coverage=false

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[codecov]

Codecov Report

Merging #7069 (b37645d) into main (f74862c) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7069   +/-   ##
=======================================
  Coverage   87.43%   87.43%           
=======================================
  Files         386      386           
  Lines       13192    13192           
  Branches     3872     3872           
=======================================
  Hits        11534    11534           
  Misses       1292     1292           
  Partials      366      366           

Flag	Coverage Δ
unittest	87.43% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/eslint-plugin/src/util/getStringLength.ts	100.00% <100.00%> (ø)

[JoshuaKGoldberg]

Super, thanks for this!

Sorry about the delay - we've been somewhat focused on v6. But I like this PR!