[SR][SR Tree] Add screen reader tree to interactive graph editor

[nishasy]

Summary:

To make it easier for content authors (and us devs while we're still
working on the screen reader experience) to build the screen reader
experience for an interactive graph without constantly having to
turn on the screen reader, add a screen reader tree directly into
the editor.

To do this, I used querySelectorAll() to get the mafs container
and all its children, and read their aria-label and
aria-describedby attributes.

After building an object with the elements, roles, and attributes,
display a tree showing these in the editor.

Issue: https://khanacademy.atlassian.net/browse/LEMS-2714

Test plan:

yarn jest packages/perseus-editor/src/widgets/interactive-graph-editor/components/interactive-graph-sr-tree.test.tsx

Storybook

• Go to http://localhost:6006/iframe.html?globals=&id=perseuseditor-widgets-interactive-graph--interactive-graph-circle&viewMode=story
• Update the whole graph aria label and description
• Update the correct graph
• Update the locked figures and their labels
• Confirm that the SR tree updates

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (47dabcf) and published it to npm. You
can install it using the tag PR2062.

Example:

yarn add @khanacademy/perseus@PR2062

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

./dev/tools/bump_perseus_version.sh -t PR2062

[github-actions]

Size Change: +950 B (+0.07%)

Total Size: 1.27 MB

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	689 kB	+948 B (+0.14%)
packages/perseus/dist/es/index.js	417 kB	+2 B (0%)

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/strings.js	4.93 kB
packages/pure-markdown/dist/es/index.js	3.67 kB
packages/simple-markdown/dist/es/index.js	12.5 kB

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