Add -all option to 'yarn clean'

[jeremywiebe]

Summary:

We've had instances where folks' local repo gets into a bad state. It's assumed that yarn clean will resolve this, but it hasn't in all cases because it doesn't delete node_modules.

This PR adds a --all option to yarn clean to demolish all node_modules folders in the local repo.

Issue: "none"

Test plan:

yarn
yarn clean
ls node_modules # still exists
yarn clean --all
find . -name node_modules -and -type d # no results!

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (86d2184) and published it to npm. You
can install it using the tag PR2176.

Example:

yarn add @khanacademy/perseus@PR2176

If you are working in Khan Academy's webapp, you can run:

./dev/tools/bump_perseus_version.sh -t PR2176

[github-actions]

Size Change: 0 B

Total Size: 1.48 MB

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	39 kB
packages/keypad-context/dist/es/index.js	760 B
packages/kmath/dist/es/index.js	86.8 kB
packages/math-input/dist/es/index.js	77.6 kB
packages/math-input/dist/es/strings.js	1.79 kB
packages/perseus-core/dist/es/index.js	43.5 kB
packages/perseus-editor/dist/es/index.js	688 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus-score/dist/es/index.js	113 kB
packages/perseus/dist/es/index.js	382 kB
packages/perseus/dist/es/strings.js	5.82 kB
packages/pure-markdown/dist/es/index.js	3.66 kB
packages/simple-markdown/dist/es/index.js	12.5 kB

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[jeremywiebe]

We could probably make an argument for not having an option at all and just deleting all node_modules folder always.

What say you?