New Skip Navigation component

[julien-deramond]

Description

This PR suggests to add a new "Skip navigation" component to our list of components.

Warning
Heavily WIP. Would need real descriptions, examples and so on.

Motivation & Context

First of all, I know that it is not a real component since it doesn't require any extra JS nor CSS, and uses only utilities. However I'm wondering if, still, it shouldn't appear as a component in Bootstrap (it could be enhanced with another example with a navbar and a default design for example).

Another option would be to have a dedicated example page but it would remain hidden in some part of the docs.

I don't have a strong opinion on it but it could maybe help propagating accessibility good practices.

I'd love to have your feedback/opinion on this idea 🙏

Type of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• All new and existing tests passed

Live previews

• Skip navigation component
• Mention in Getting Started > Accessibility > Visually hidden content
• Mention in Helpers > Visually hidden