Upgrade Storybook v8.x

[mark-fitzgerald]

Summary:

Nothing is broken. Everything is happy.

Test plan:

yarn start is happy
yarn build-storybook; python3 -m http.server -d storybook-static; -> open http://localhost:8000 in a browser
yarn build-storybook --stats-json works and generates /storybook-static/preview-stats.json
yarn dev is happy

[github-actions]

Size Change: -99 B (-0.01%)

Total Size: 1.29 MB

Filename	Size	Change
packages/kas/dist/es/index.js	39 kB	+5 B (+0.01%)
packages/math-input/dist/es/index.js	77.9 kB	-3 B (0%)
packages/perseus-editor/dist/es/index.js	698 kB	-60 B (-0.01%)
packages/perseus-linter/dist/es/index.js	22.2 kB	-2 B (-0.01%)
packages/perseus/dist/es/index.js	425 kB	-38 B (-0.01%)
packages/simple-markdown/dist/es/index.js	12.5 kB	-1 B (-0.01%)

ℹ️ View Unchanged

Filename	Size
packages/keypad-context/dist/es/index.js	760 B
packages/kmath/dist/es/index.js	4.27 kB
packages/math-input/dist/es/strings.js	1.79 kB
packages/perseus-core/dist/es/index.js	1.48 kB
packages/perseus/dist/es/strings.js	3.57 kB
packages/pure-markdown/dist/es/index.js	3.66 kB

_{compressed-size-action}

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (015acb1) and published it to npm. You
can install it using the tag PR1904.

Example:

yarn add @khanacademy/perseus@PR1904

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

./dev/tools/bump_perseus_version.sh -t PR1904