feat(theme-common): JSDoc for all APIs

[Josh-Cena]

Motivation

Make our API much more approachable and stable-appearing.

Have you read the Contributing Guidelines on pull requests?

Yes

[netlify]

✅ [V2]

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	72
🟢 Accessibility	100
🟢 Best practices	92
🟢 SEO	100
🟢 PWA	90

Lighthouse ran on https://deploy-preview-6974--docusaurus-2.netlify.app/

[github-actions]

Size Change: -140 B (0%)

Total Size: 805 kB

Filename	Size	Change
website/build/assets/js/main.********.js	612 kB	-140 B (0%)

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	49.9 kB
website/build/assets/css/styles.********.css	105 kB
website/build/index.html	38.8 kB

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