[Preview NG] Add exercise content variant to typed preview protocol

[jeremywiebe]

Summary:

Adds an "exercise" variant to the typed preview protocol to support the full-exercise preview view.

Note that there is no preview rendering of this new type as that is (and will continue to be) handled by the consuming apps. This just plumbs the value through for use.

Issue: LEMS-3741

Test plan:

• pnpm test
• pnpm tsc

[github-actions]

Size Change: +6 B (0%)

Total Size: 508 kB

📦 View Changed

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	105 kB	+6 B (+0.01%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.6 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/kmath/dist/es/index.js	6.32 kB
packages/math-input/dist/es/index.js	98.5 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.item-splitting.js	12 kB
packages/perseus-core/dist/es/index.js	26.3 kB
packages/perseus-linter/dist/es/index.js	9.8 kB
packages/perseus-score/dist/es/index.js	10.2 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/perseus/dist/es/index.js	200 kB
packages/perseus/dist/es/strings.js	8.6 kB
packages/pure-markdown/dist/es/index.js	1.39 kB
packages/simple-markdown/dist/es/index.js	6.71 kB

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[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (d89d5fd) and published it to npm. You
can install it using the tag PR3762.

Example:

pnpm add @khanacademy/perseus@PR3762

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

./dev/tools/bump_perseus_version.ts -t PR3762

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

./dev/tools/bump_perseus_version.js -t PR3762