fix(theme-common): use native scrolling when smooth behavior set in CSS

[Josh-Cena]

Motivation

Part of the changes in #6666

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Add scroll-behavior: smooth to the root selector

Before	After

Related PRs

[netlify]

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	56
🟢 Accessibility	100
🟢 Best practices	92
🟢 SEO	100
🟢 PWA	90

Lighthouse ran on https://deploy-preview-7057--docusaurus-2.netlify.app/

[github-actions]

Size Change: +190 B (0%)

Total Size: 807 kB

Filename	Size	Change
website/build/assets/js/main.********.js	613 kB	+190 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	38.4 kB

_{compressed-size-action}

[slorber]

FYI smooth behavior was added to Safari recently so hopefully the polyfill can be removed soon!

https://caniuse.com/?search=scroll-behavior