Add API for requesting add TileService

This CL adds the API to StatusBarManager, as well as the constants. It
also wires things into SystemUI so the API actually works as intended.

TODO:
  * Rate limit requests (b/197534249)

Fixes: 197207978
Test: manual using test app
Test: atest SystemUITests

Change-Id: I2a9d18535fde1d77e9d6792bd45002ce04b49dab