WIP: Make exercise editor preview (right side) sticky

[nishasy]

Summary:

Issue: XXX-XXXX

Test plan:

[khan-actions-bot]

Gerald

Required Reviewers

• @Khan/perseus for changes to .changeset/metal-ties-boil.md, packages/perseus-editor/src/components/device-framer.tsx, packages/perseus-editor/src/styles/perseus-editor.less

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[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (d15ce44) and published it to npm. You
can install it using the tag PR1286.

Example:

yarn add @khanacademy/perseus@PR1286

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

./dev/tools/bump_perseus_version.sh -t PR1286

[github-actions]

Size Change: +28 B (0%)

Total Size: 841 kB

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	269 kB	-3 B (0%)
packages/perseus/dist/es/index.js	404 kB	+31 B (+0.01%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	38.1 kB
packages/kmath/dist/es/index.js	4.27 kB
packages/math-input/dist/es/index.js	80.5 kB
packages/math-input/dist/es/strings.js	1.73 kB
packages/perseus-core/dist/es/index.js	908 B
packages/perseus-error/dist/es/index.js	877 B
packages/perseus-linter/dist/es/index.js	21.8 kB
packages/perseus/dist/es/strings.js	3.22 kB
packages/pure-markdown/dist/es/index.js	3.68 kB
packages/simple-markdown/dist/es/index.js	12.4 kB

_{compressed-size-action}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.41%. Comparing base (b02eaef) to head (d15ce44).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1286      +/-   ##
==========================================
+ Coverage   69.10%   70.41%   +1.30%     
==========================================
  Files         480      485       +5     
  Lines      102322   102410      +88     
  Branches     7309    11003    +3694     
==========================================
+ Hits        70710    72111    +1401     
+ Misses      31497    30299    -1198     
+ Partials      115        0     -115     

Files	Coverage Δ
...es/perseus-editor/src/components/device-framer.tsx	88.17% <ø> (-0.13%)	⬇️

... and 140 files with indirect coverage changes

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