Improved collapsed messaging notifications

Previously the messaging layout was working on a fixed
Height, which didn't scale well as we were now using it
also in the collapsed version.
For big text notifications, the view would be
clipped ugly, since we were using a fixed number of
lines. Instead we're now calculating this dynamically.

Fixes: 35126759
Test: runtest systemui
Change-Id: Ie3736d807d7a162ee51ad65794bf2f1cfb2248be