Static site editor syntax coloring/highlighting

Revisit the approach for ensuring the Static site editor has consistent editor styling with other GitLab editors. A few notes:

• At time of this writing the ACE editor has a deprecation plan
• We may consider leveraging the Monoco editor in the SSE for Markdown mode

We can still update the current Toast UI Editor that the SSE uses, but I'm hesitant based on the two above comments.

If the latter occurs, we get this styling for free.

Added context: !35347 (comment 371233055)