fix(isLength): added process to subtract Presentation Sequences characters

[ikkyu-3]

#1941

• Added process to subtract presentation sequence characters from total characters
• Edited test

https://unicode.org/reports/tr51/#Emoji_Variation_Sequences

Checklist

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

[codecov]

Codecov Report

Merging #1967 (95345ae) into master (cfcf911) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1967   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          103       103           
  Lines         2097      2098    +1     
  Branches       473       474    +1     
=========================================
+ Hits          2097      2098    +1     

Impacted Files	Coverage Δ
src/lib/isLength.js	100.00% <100.00%> (ø)

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[rubiin]

Thankyou for the contribution 🎉