feat: allow reporters to be default exports

[SimenB]

Summary

Way nicer if the reporter is transpiled

Test plan

Green CI

[codecov-io]

Codecov Report

Merging #9161 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #9161   +/-   ##
=======================================
  Coverage   64.83%   64.83%           
=======================================
  Files         279      278    -1     
  Lines       11733    11733           
  Branches     2883     2882    -1     
=======================================
  Hits         7607     7607           
  Misses       3509     3509           
  Partials      617      617

Impacted Files	Coverage Δ
packages/jest-core/src/TestScheduler.ts	64.92% <0%> (-0.49%)	⬇️
packages/jest-config/src/normalize.ts	81.17% <0%> (ø)	⬆️
packages/jest-reporters/src/index.ts

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[jeysal]

Nice, add to custom-reporters e2e similar to setup, teardown, environment?

[github-actions]

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