[Connected Displays in Taskbar] Refactor TaskbarDelegate for Display Signals

Refactor the TaskbarDelegate to support multiple pass down displayId specific signals down to the taskbar level.

Flag: EXEMPT not adding new behavior
Bug: 376128251
Test: Manual
Change-Id: I41ec5c394adb2e804aedf189c8f57fd2c8d84366
3 files changed