Adds isEmoji validator

[samilieberman]

Adds isEmoji validator

Checklist

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

Test Coverage

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (72573b3) to head (4695a84).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2575   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       115    +1     
  Lines         2535      2542    +7     
  Branches       641       642    +1     
=========================================
+ Hits          2535      2542    +7     

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[samilieberman]

@rubiin @profnandaa @tux-tn @WikiRik It's not allowing me to add reviewers to my PR. Are you able to take a look?