Support TypeScript typecasts

[joshkel]

Why am I submitting this PR

Add support for TypeScript typecasts within JSX expressions.

Does it fix an existing ticket?

Yes - #603

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• tests are included and pass: yarn test (see details here)
• documentation is changed or added

[codecov-commenter]

Codecov Report

Merging #604 (dbe5156) into master (67cf845) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #604      +/-   ##
==========================================
+ Coverage   95.34%   95.36%   +0.01%     
==========================================
  Files          11       11              
  Lines        1633     1640       +7     
==========================================
+ Hits         1557     1564       +7     
  Misses         76       76              

Impacted Files	Coverage Δ
src/lexers/jsx-lexer.js	98.11% <100.00%> (+0.05%)	⬆️

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[karellm]

Deployed as part of 6.6.0. Thanks!