Alias v26 round icons to adaptive icons like aapt1

When a developer specifies an adaptive application icon,
and a non-adaptive round application icon, create an alias
from the round icon to the regular icon for v26 APIs and up.

We do this because certain devices prefer android:roundIcon over
android:icon regardless of the API levels of the drawables set for
either.

This auto-aliasing behaviour allows an app to prefer the
android:roundIcon on API 25 devices, and prefer the adaptive icon on
API 26 devices.

Bug: 34829129
Test: manual
Change-Id: Ifac49455da749afde636fd4bb8cf32308f8b1e0a