Update dropdown labeling guidance to internal article

[marcysutton]

Summary:

I got feedback from the Content team that the w3c-WAI article linked from the editor was too technical for the audience. So I created an internal doc that we can maintain, that also links to the previous article for those who are curious.

Issue: FEI-6288

Test plan:

1. Ensure the links work (the doc is on Confluence)
2. Ensure the link text fits ("this internal article" instead of "this article")

[github-actions]

Size Change: +20 B (0%)

Total Size: 471 kB

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	89.6 kB	+20 B (+0.02%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.7 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/kmath/dist/es/index.js	5.98 kB
packages/math-input/dist/es/index.js	98.6 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.js	19.4 kB
packages/perseus-linter/dist/es/index.js	7.05 kB
packages/perseus-score/dist/es/index.js	9.15 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/perseus/dist/es/index.js	202 kB
packages/perseus/dist/es/strings.js	7.61 kB
packages/pure-markdown/dist/es/index.js	1.22 kB
packages/simple-markdown/dist/es/index.js	6.72 kB

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[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (8503d21) and published it to npm. You
can install it using the tag PR2504.

Example:

pnpm add @khanacademy/perseus@PR2504

If you are working in Khan Academy's webapp, you can run the below command.
If this is for backend code, change the static flag (-s) from y/yes to n/no.

./dev/tools/bump_perseus_version.js -s y -t PR2504

[marcysutton]

My one question is: can we link to an internal article in this project? Or am I not adequately considering external audiences since this is an OS project?