[Numeric Input] Update UI of editor

[mark-fitzgerald]

Summary:

Issue: LEMS-2456

Test plan:

[github-actions]

Size Change: +2 kB (+0.16%)

Total Size: 1.27 MB

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	690 kB	+2 kB (+0.29%)

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	4.27 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	1.48 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus/dist/es/index.js	416 kB
packages/perseus/dist/es/strings.js	4.12 kB
packages/pure-markdown/dist/es/index.js	3.67 kB
packages/simple-markdown/dist/es/index.js	12.5 kB

_{compressed-size-action}

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (b3c8124) and published it to npm. You
can install it using the tag PR2015.

Example:

yarn add @khanacademy/perseus@PR2015

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

./dev/tools/bump_perseus_version.sh -t PR2015