feat(jest-snapshot): migrate to ESM

[SimenB]

Summary

Bundling doesn't like export =, so let's get rid of it.

I also cleanup up the exports a bit (not exporting utils)

Test plan

Green CI

[codecov-commenter]

Codecov Report

Merging #12342 (ae60d1b) into main (f2e3040) will increase coverage by 0.00%.
The diff coverage is 71.42%.

@@           Coverage Diff           @@
##             main   #12342   +/-   ##
=======================================
  Coverage   66.97%   66.97%           
=======================================
  Files         329      329           
  Lines       17338    17336    -2     
  Branches     5066     5066           
=======================================
- Hits        11612    11611    -1     
+ Misses       5694     5693    -1     
  Partials       32       32           

Impacted Files	Coverage Δ
...circus/src/legacy-code-todo-rewrite/jestAdapter.ts	0.00% <ø> (ø)
...us/src/legacy-code-todo-rewrite/jestAdapterInit.ts	0.00% <0.00%> (ø)
packages/jest-jasmine2/src/index.ts	0.00% <0.00%> (ø)
packages/jest-jasmine2/src/setup_jest_globals.ts	0.00% <0.00%> (ø)
packages/jest-runtime/src/index.ts	55.32% <ø> (ø)
packages/jest-core/src/TestScheduler.ts	81.08% <100.00%> (ø)
packages/jest-snapshot/src/index.ts	78.75% <100.00%> (-0.14%)	⬇️

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