Do not use React svg components for regularly used icons

### Have you read the Contributing Guidelines on issues?

- [X] I have read the [Contributing Guidelines on issues](https://github.com/facebook/docusaurus/blob/main/CONTRIBUTING.md#reporting-new-issues).

### Motivation

This issue about updating the number of visible archived versions in the version dropdown lead to a weird build size diff on HTML files:

https://github.com/facebook/docusaurus/pull/5862#issuecomment-958881323

The diff in size is due to using an inlined SVG component for external links 😅 the SVG markup is duplicated in the HTML file for each item


For reusable icons of our theme, we should rather require an `svg` file instead of using a React SVG component, to reduce HTML output size.

It can have a significant impact on pages with a lot of icons (due to navbar, footer, doc sidebar...)

### Self-service

- [ ] I'd be willing to do some initial work on this proposal myself.