Add a config to force rounded icon for DashboardFragment.

And each page has ability to turn on/off rounded icons. This CL only
adds the flag, it doesn't actually change icon shape yet.

- Boolean config in xml
- New protected method for each DashboardFragment to load config
- Plumb the boolean into DashboardFeatureProvider for future use.
- Remove some unused APIs from DashboardFeatureProvider

Bug: 110405144
Fixes: 79748104
Test: robotests
Change-Id: Id34782e75aa7289967e4dd1f4fe2978688092702