Add a growth broadcast receiver in taskbar.

The growth broadcast receiver will be used to receive broadcast from
Growth Framework and show a nudge on screen.

Refer to go/al-growth-framework-nudge

Test: Manual
Bug: b/396165728
Flag: com.android.launcher3.enable_growth_nudge
Change-Id: Iebf006c733f6f9d079a4c3b03d78fb7c9dd3e5e7