POC: migrate expression widget to latest version in PerseusItem parser

[benchristel]

This demonstrates how we can upgrade/migrate widget options in the parsing
code, obviating the need for propUpgrades.

The fact that version is an object makes this really annoying because
TypeScript can't discriminate unions based on nested properties like
version.major. Given that constraint, I think the approach I came up with is
reasonable, but I'm certainly open to feedback on how to improve it.

Issue: LEMS-2582

Test plan:

yarn test

[khan-actions-bot]

Gerald

Required Reviewers

• @Khan/perseus for changes to packages/perseus/src/util/parse-perseus-json/perseus-parsers/expression-widget.test.ts, packages/perseus/src/util/parse-perseus-json/perseus-parsers/expression-widget.ts, packages/perseus/src/util/parse-perseus-json/perseus-parsers/widget.ts

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[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (527be33) and published it to npm. You
can install it using the tag PR1908.

Example:

yarn add @khanacademy/perseus@PR1908

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

./dev/tools/bump_perseus_version.sh -t PR1908

[github-actions]

Size Change: +237 B (+0.02%)

Total Size: 1.29 MB

Filename	Size	Change
packages/perseus/dist/es/index.js	425 kB	+237 B (+0.06%)

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	698 kB
packages/perseus-linter/dist/es/index.js	22.2 kB
packages/perseus/dist/es/strings.js	3.57 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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