Convert sprite-animated to TypeScript

[Zyie]

Description of change

Another simple conversion.

• Made playing a get only property to keep it readonly

Pre-Merge Checklist

• Lint process passed (npm run lint)
• Tests passed (npm run test)

[codecov-io]

Codecov Report

Merging #6397 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #6397   +/-   ##
=======================================
  Coverage   76.85%   76.85%           
=======================================
  Files          69       69           
  Lines        3910     3910           
=======================================
  Hits         3005     3005           
  Misses        905      905

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[bigtimebuddy]

Thanks again @Zyie, you're killing it at the TS conversion