feat(Dropdown): add 'closeOnEscape' prop

[mcmxcdev]

Fixes #3622.

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• Run yarn lint locally to catch formatting errors. This will fix some errors automatically, commit and push any changes.
• Run yarn test locally to catch errors. This ensures all components still behave as they should.
• Run yarn start to run the doc site locally and try a few pages, ensuring everything is in good working order.
• Include tests when adding/changing behavior.

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[codecov-io]

Codecov Report

Merging #3632 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3632      +/-   ##
==========================================
+ Coverage   99.81%   99.81%   +<.01%     
==========================================
  Files         174      174              
  Lines        2747     2749       +2     
==========================================
+ Hits         2742     2744       +2     
  Misses          5        5

Impacted Files	Coverage Δ
src/modules/Dropdown/Dropdown.js	100% <100%> (ø)	⬆️

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[layershifter]

❤️

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉