let transformers adjust cache key based on mapCoverage

[jwbay]

Summary
The first time someone flips on mapCoverage, they'll have a bad time if their transformer implements a getCacheKey since the flag is not passed to it. There's a chance this PR would fix issues like #4163. I ran into something similar and nuking the cache manually fixed it.

Test plan
Test added

[codecov-io]

Codecov Report

Merging #4187 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4187   +/-   ##
=======================================
  Coverage   60.25%   60.25%           
=======================================
  Files         198      198           
  Lines        6781     6781           
  Branches        6        6           
=======================================
  Hits         4086     4086           
  Misses       2692     2692           
  Partials        3        3

Impacted Files	Coverage Δ
packages/jest-runtime/src/script_transformer.js	89.92% <ø> (ø)	⬆️

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[thymikee]

looks good

[github-actions]

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