CodeMirror Blob: improve highlighting for Markdown, CSS, XML, HTML, TSX, TypeScript, JavaScript, JSX

Created by: olafurpg

Further CSS color changes for the syntax highlighting with the new CodeMirror Blob.

Towards https://github.com/sourcegraph/sourcegraph/issues/40551

Test plan

See updated snapshot tests.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.