Allow keyboard navigation of images

[SonicScrewdriver]

Summary:

This PR allows the keyboard navigation of our images so that users can easily interact with the zoom functionality. I have also added the spacebar and enter keys as optional methods for closing the image, just to help avoid any confusion for our users.

Issue: LEMS-2697

Test plan:

• manual testing
• a new test that I should add tomorrow morning.

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (4ecee88) and published it to npm. You
can install it using the tag PR1990.

Example:

yarn add @khanacademy/perseus@PR1990

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

./dev/tools/bump_perseus_version.sh -t PR1990

[github-actions]

Size Change: +48 B (0%)

Total Size: 1.27 MB

Filename	Size	Change
packages/perseus/dist/es/index.js	415 kB	+48 B (+0.01%)

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	77.9 kB
packages/math-input/dist/es/strings.js	1.79 kB
packages/perseus-core/dist/es/index.js	1.48 kB
packages/perseus-editor/dist/es/index.js	688 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus/dist/es/strings.js	3.7 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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[mark-fitzgerald]

Verified functionality in Storybook (with zoomed image).