Mutate DrawableContainer children immediately after inflation

Previously we would only mutate children when they were displayed, so
applyTheme() calls would be applied to the shared constant state. Now
we mutate() immediately after obtaining the child, which ensures we
have a clean constant state. This also allows us to remove extra
mutate() calls, since we know all child drawables are already mutated.

Bug: 25081461
Change-Id: I52390db268690a8e181f5b9bbe612b7ed6ce9359