[Status bar] Clarify the API between TileServices and status bar icons.

This CL re-names the StatusBarIconController APIs that are only used by
TileServices to specifically have "tile" in them. Then, it's obvious why
the implementation of the method considers those icons external instead
of internal.

This also fixes two  bugs with the tile status bar icons. See first
two linked bug fixes.

Fixes: 273536393
Fixes: 273540833
Bug: 265307726

Test: Add tile service that has status icon -> verify icon is added (see
b/265307726 for demo)
Test: Remove tile service that has status icon -> verify icon is rmeoved
(see b/265307726 for demo)
Test: verify tile status icon is correct size
Test: atest StatusBarIconControllerImplTest

Change-Id: Ieac39be633e85ce5076272f9afc12f953839bedc