Move scoring logic: CSProgram, Iframe, and Dropdown

[handeyeco]

Summary:

Decided to do 3, since they're all pretty simple

• CSProgram
• Iframe
• Dropdown

Issue: LEMS-2737

Test plan:

Nothing should change, moving code

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (5b72ed9) and published it to npm. You
can install it using the tag PR2111.

Example:

yarn add @khanacademy/perseus@PR2111

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

./dev/tools/bump_perseus_version.sh -t PR2111

[github-actions]

Size Change: -90 B (-0.01%)

Total Size: 1.47 MB

Filename	Size	Change
packages/perseus-score/dist/es/index.js	107 kB	+299 B (+0.28%)
packages/perseus/dist/es/index.js	407 kB	-389 B (-0.1%)

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	83.1 kB
packages/math-input/dist/es/index.js	78 kB
packages/math-input/dist/es/strings.js	1.79 kB
packages/perseus-core/dist/es/index.js	23.1 kB
packages/perseus-editor/dist/es/index.js	689 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus/dist/es/strings.js	4.85 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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