Prototype aria-live for interactive graphs

[benchristel]

DO NOT LAND

Test plan:

TODO

[khan-actions-bot]

Gerald

Required Reviewers

• @Khan/perseus for changes to packages/perseus/src/widgets/interactive-graphs/ariaLiveAnnounce.ts, packages/perseus/src/widgets/interactive-graphs/types.ts, packages/perseus/src/widgets/interactive-graphs/graphs/point.tsx, packages/perseus/src/widgets/interactive-graphs/reducer/interactive-graph-reducer.ts

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[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (c4bbbcb) and published it to npm. You
can install it using the tag PR1960.

Example:

yarn add @khanacademy/perseus@PR1960

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

./dev/tools/bump_perseus_version.sh -t PR1960

[github-actions]

Size Change: +320 B (+0.02%)

Total Size: 1.29 MB

Filename	Size	Change
packages/perseus/dist/es/index.js	423 kB	+320 B (+0.08%)

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	697 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus/dist/es/strings.js	3.99 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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