Use BaseIconFactory to create app icon bitmap.

Introduces BaseIconFactory to caption to create a bitmap to use
for caption's app icon, compressing it more smoothly.

Change of 24 -> 28 dp for the icon ImageView is to compensate for the
mild shrinkage caused by BaseIconFactory.

Before: https://screenshot.googleplex.com/moyzAhDnMiAJuE8.png
After: https://screenshot.googleplex.com/3SA4a6Cj3wrfFoo.png
Bug: 296921992
Test: Manual
Change-Id: Ia5579338e3f9b2142445c56c391cfc216b03ffc5