[CSS] Break Perseus styling into its own Cascade Layers

[mark-fitzgerald]

Summary:

Issue: LEMS-3761

Test plan:

[github-actions]

🗄️ Schema Change: No Changes ✅

[github-actions]

🛠️ Item Splitting: No Changes ✅

[github-actions]

Size Change: 0 B

Total Size: 499 kB

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.8 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/kmath/dist/es/index.js	5.98 kB
packages/math-input/dist/es/index.js	99.2 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.item-splitting.js	13.1 kB
packages/perseus-core/dist/es/index.js	25.4 kB
packages/perseus-editor/dist/es/index.js	97.7 kB
packages/perseus-linter/dist/es/index.js	8.64 kB
packages/perseus-score/dist/es/index.js	9.2 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/perseus/dist/es/index.js	200 kB
packages/perseus/dist/es/strings.js	7.73 kB
packages/pure-markdown/dist/es/index.js	1.39 kB
packages/simple-markdown/dist/es/index.js	6.72 kB

_{compressed-size-action}

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (857b7ad) and published it to npm. You
can install it using the tag PR3113.

Example:

pnpm add @khanacademy/perseus@PR3113

If you are working in Khan Academy's frontend, you can run the below command.

./dev/tools/bump_perseus_version.ts -t PR3113

If you are working in Khan Academy's webapp, you can run the below command.

./dev/tools/bump_perseus_version.js -t PR3113