chore: run all tests in pre-commit hook to avoid 'No tests found' error

[TrevorBurnham]

What:

When trying to commit changes, I noticed that the precommit hook failed with this error:

No tests found, exiting with code 1
Run with `--passWithNoTests` to exit with code 0

The root cause appears to be a known bug in Jest's --findRelatedTests feature: jestjs/jest#11527 That flag is incompatible with the roots configuration option, which kcd-scripts uses.

The fix here is to use a custom lint-staged.config.js to replace the one from kcd-scripts.

Fixes #696

Why:

With the current pre-commit hook, contributors may have to use --no-verify to commit their changes. That adds a significant amount of friction to contributions, and also means that those contributions won't benefit from being linted and formatted via lint-staged.

How:

The custom lint-staged.config.js is equivalent to the one from kcd-scripts, but without the --findRelatedTests flag. Since all of this repo's tests take only a few seconds to run, I don't think this is overly burdensome.

I've also removed the watchPlugins config options from the Jest config to address "Unknown option" validation warnings emitted when running the tests. See #696 for example output.

Lastly, I've added .jest-cache/ to .gitignore, as I noticed that files were being created there.

Checklist:

• Documentation - N/A
• Tests
• Updated Type Definitions - N/A
• Ready to be merged