refactor: use CSS Modules for toggle styles

[lex111]

Breaking Changes:

• Former react-toggle classes have been removed in favor of css module classes (with hash). This may break some custom CSS selectors you have if you customized the toggle with CSS classes.

Motivation

Resolves #5586

Although this would require changes to styles of sites with toggle customization, it is a better approach that is consistent with our other components.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Preview

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

[netlify]

✔️ [V2]

🔨 Explore the source changes: f2679e0

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/614825af7d914400077d29dc

😎 Browse the preview: https://deploy-preview-5592--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	80
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-5592--docusaurus-2.netlify.app/

[github-actions]

Size Change: -98 B (0%)

Total Size: 826 kB

Filename	Size	Change
website/build/assets/css/styles.********.css	94 kB	-38 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
website/.docusaurus/globalData.json	36.7 kB	0 B
website/build/assets/js/main.********.js	414 kB	0 B
website/build/blog/2017/12/14/introducing-docusaurus/index.html	67 kB	-8 B (0%)
website/build/blog/index.html	38.1 kB	-8 B (0%)
website/build/docs/index.html	44.5 kB	-10 B (0%)
website/build/docs/installation/index.html	52.8 kB	-10 B (0%)
website/build/index.html	30.8 kB	-8 B (0%)
website/build/tests/docs/index.html	25.4 kB	-8 B (0%)
website/build/tests/docs/standalone/index.html	23 kB	-8 B (0%)

_{compressed-size-action}

[slorber]

Thanks, LGTM 👍