Create new SDC component for Umami Branding

Problem/Motivation

Single directory components (SDC) is a new way to theme Drupal. Instead of scattering related files around your theme, they're contained to one directory. The primary issue for SDC is at #3313520: Single directory components in core.

The Demo Umami team has decided that their theme can depend on an experimental module like SDC. This allows us to have the work in this ticket merged even when #3352256: [META] Move code from the experimental SDC module to core is not committed.

Branding component

As part of SDC's roadmap (see #3345922: Single Directory Components module roadmap: the path to beta and stable), we want to convert Umami components to use SDC. For this task I'm choosing the Branding component, which includes markup and CSS.

This component is a good fit because: it is simple and fairly modular styling already

This component involves the following Twig templates, CSS, assets, and libraries:

1. branding.css
2. block--system-branding-block.html.twig

Testing instructions

1. Set up site with Umami profile
2. View page and see that logo is visible
3. Inspect markup with twig debug enabled and verify that component is being used `
   

   `

4. Check the theme settings and verify that the component works with the different settings, such as adding a site slogan, disabling the logo image, etc...