Update all packages + replace Enzyme with Testing Library

[WesCossick]

This PR updates all the packages in this repo to the latest available versions. Additionally, I've replaced Enzyme with Testing Library and applied some of our company's newer design patterns to the tests.

Note: The migration to Testing Library is not fully complete; the @testing-library/user-event package does not currently support arrow up/down keys. @corymharper is looking into submitting a PR to their repo to add this functionality.

[codecov]

Codecov Report

Merging #215 (55145f5) into master (284c3b0) will increase coverage by 2.38%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #215      +/-   ##
==========================================
+ Coverage   82.14%   84.52%   +2.38%     
==========================================
  Files           1        1              
  Lines          84       84              
  Branches       22       22              
==========================================
+ Hits           69       71       +2     
+ Misses         15       13       -2     

Impacted Files	Coverage Δ
src/use-dropdown-menu.ts	84.52% <100.00%> (+2.38%)	⬆️

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[WesCossick]

I went ahead and used fireEvent() directly for any tests that need to use up/down arrow keys. We may end up using @testing-library/user-event in the future if they add support for up/down arrow keys.