codemirror blob: Restructure syntax extension to share blob info

Created by: fkling

Best reviewed with white-space difference turned off.

This commit refactors the syntax extension to provide a "blob" field that holds the information about the current blob and derives syntax highlighting information from that field via a facet instead.

This way the blob field can be used by other extensions, e.g. for hovercards.

Test plan

Syntax highlighting works as before.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.