feat: TypeScript presets/plugins should expose Options typing

[slorber]

Motivation

• Each TS plugin should expose an Options type
• Each preset (only one actually) should re-expose underlying plugin options + ThemeConfig
• Site configs can consume those exported types for IDE auto-completion with JSDoc annotations
• Temporarily disable bootstrap theme integration / TS typechecking (we might even delete it someday?)

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

IDE autocompletion works

[Josh-Cena]

Can we also move plugin-content-blog/index.d.ts to plugin-content-blog/src/plugin-content-blog.d.ts? The only type definition that's in a different place.

[slorber]

Yes just moved it.

All these TS files are not very organized currently, we'll need to do further cleanup 🤪

[netlify]

✔️ [V2]

🔨 Explore the source changes: 468b541

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/612f4408d8eca6000710d975

😎 Browse the preview: https://deploy-preview-5456--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	86
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-5456--docusaurus-2.netlify.app/

[github-actions]

Size Change: -2 B (0%)

Total Size: 822 kB

ℹ️ View Unchanged

Filename	Size	Change
website/.docusaurus/globalData.json	36.5 kB	0 B
website/build/assets/css/styles.********.css	93.7 kB	0 B
website/build/assets/js/main.********.js	412 kB	0 B
website/build/blog/2017/12/14/introducing-docusaurus/index.html	66.8 kB	0 B
website/build/blog/index.html	37.6 kB	0 B
website/build/docs/index.html	44.7 kB	-1 B (0%)
website/build/docs/installation/index.html	52.7 kB	-1 B (0%)
website/build/index.html	30.4 kB	0 B
website/build/tests/docs/index.html	25 kB	0 B
website/build/tests/docs/standalone/index.html	22.6 kB	0 B

_{compressed-size-action}