Add "External" arrow on all external links, not only sidebar

[miketheman]

Hi there!

I'm finding the desire to have the little external arrow for inline docs, not only the sidebar.

furo/src/furo/assets/styles/components/_sidebar.sass

Lines 139 to 144 in 0188705

	// Add a nice little "external-link" arrow here.
	&.external::after
	content: url('data:image/svg+xml,<svg width="12" height="12" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="1.5" stroke="%23607D8B" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z"/><path d="M11 7h-5a2 2 0 0 0 -2 2v9a2 2 0 0 0 2 2h9a2 2 0 0 0 2 -2v-5" /><line x1="10" y1="14" x2="20" y2="4" /><polyline points="15 4 20 4 20 9" /></svg>')
	margin: 0 0.25rem
	vertical-align: middle
	color: var(--color-sidebar-link-text)

It'd be great to have the ability to discern if the link I'm about to click will remain within a docs site, or if it'll take me away from it.

Would you consider a change to the lower-level CSS that uses this code more liberally?

If so, can you point me where that might live? Happy to submit a PR.