Related RFC

Description

We should allow Up Down Left Right arrow key navigation in the blob view.

Acceptance criteria:

• Up/Down navigation works in ALL files (even those without code intelligence)
  • Should just change the visible "focused" line, when clicked it should navigate to this line
• Left/Right navigation works in files with code intelligence.
  • Should allow cycling between tokens on a specific line. Allows for 1 handed keyboard nav in the blob view.

Implementation

WIP Here: https://github.com/sourcegraph/sourcegraph/pull/42980

/cc @felixfbecker/frontend-platform