Sharesheet - make loading placeholders unclickable

The AVD used to animate loading ds targets is build using a
square with a ds shaped cutout. Ripples on touch that go below
the AVD show a square bounding box. This looks awful, prevent
ripples as clicking the placeholder does nothing anyway.

Fixes: 129979593
Test: visual inspection
Change-Id: Id8734f3d92bd104097a60a6aa411be71db3e4efe