CodeMirror Blob: make syntax highlighting more usable

Created by: olafurpg

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

This is the first conscious effort to close the gap on syntax highlighting colors between the old and new blob view. This commit only addressed the most obvious differences for Go, TypeScript, JSON and YAML. There are other differences that will need to be addressed separately.

Test plan

Open a Go, TypeScript, YAML, and JSON file and manually verify that the colors are improved by this PR.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.