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 changed slightly but should be more powerful now (it's consistent with r <string>).
• Jumped to s <symbol> and s <context>-><symbol>.
• Jumped to d.
• Jumped to f.
• Jumped to t.
• Jumped to T123, D123, @dog, PHID-DREV-abcd, etc.

Maniphest Tasks: T13079

Differential Revision: https://secure.phabricator.com/D19088