Fix jest-mock fn and spyOn.

[cpojer]

Summary

The fn and spyOn exports for jest-mock are broken in Jest 27, see:

This PR fixes it.

Test plan

Added a new test.

[codecov-commenter]

Codecov Report

Merging #11480 (d9fb9ac) into master (e9802d3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #11480   +/-   ##
=======================================
  Coverage   68.94%   68.94%           
=======================================
  Files         312      312           
  Lines       16309    16309           
  Branches     4721     4721           
=======================================
  Hits        11245    11245           
  Misses       5036     5036           
  Partials       28       28           

Impacted Files	Coverage Δ
packages/jest-mock/src/index.ts	84.98% <100.00%> (ø)

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[SimenB]

👍

[github-actions]

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