R1:4bccb1547d6b

Modularize the "jump nav" behaviors in global search

Summary: Depends on D19087. Ref T13079. This still doesn't feel like the most clean, general system in the world, but is a step forward from hard-coded `switch()` stuff.

Test Plan:
- Jumped to `r`.
- Jumped to `a`.
- Jumped to `r poe` (multiple results).
- Jumped to `r poetry` (one result).
- Jumped to `r syzygy` (no results).
- Jumped to `p`.
- Jumped to `p robot` (multiple results); `p assessment` (one result).
- The behavior for `p <string>` has…