feat(isAlpha, isAlphanumeric): added support for Irish fadas (accents)

[khoait]

Irish fadas reference:
https://en.wikipedia.org/wiki/Irish_orthography#Vowels

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.95%. Comparing base (b958bd7) to head (42d2012).
Report is 17 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2281   +/-   ##
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  Coverage   99.95%   99.95%           
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  Files         107      107           
  Lines        2454     2454           
  Branches      619      619           
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  Hits         2453     2453           
  Partials        1        1           

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