js-test-runner: Add WorDBless dir to jest collectCoverageFrom

[anomiex]

Changes proposed in this Pull Request:

The coverage report started taking an extra 10 minutes after
packages/my-jetpack added JS tests because it was reporting coverage for
all of WordPress that was brought in via WorDBless. Exclude that by
default.

Also exclude the jetpack_vendor/ directory from
packages/composer-plugin for good measure.

Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• In the "Tests / Code coverage" job, check that the JS tests for packages/my-jetpack take closer to 5 seconds than 580.
  • ✔️ 5.738s

[github-actions]

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