Sharesheet - force DS icons to be round

DS icons cannot be provided as AdaptiveIcons. Most today are
provided as a circular bitmap but there is no shape guarantee.
To provide visual consistency, scale and mask all DS icons to a
circle. Currently, all DS icons are shaped making them hard to
see.

Fixes: 129980123
Test: manual images large and small, rectangular, circular, etc
Change-Id: I011b35c1334affb1224f62beafd3f72026198054