Better FloatingToolbar positioning.

-The toolbar is now rendered over the IME.
-The toolbar respects the presence of the IME and tries as much as
 possible not to obstruct it.
-The toolbar may obstruct the IME if there is limited space and we
 can't find a position that won't obstruct the IME.

*A side effect of the toolbar over the IME is that TextView handles
 will also always be rendered over the IME where necessary. This was
 the previous behavior before the regression.

Bug: 17510971
Change-Id: I26a49565bf025d7c007ba6bb80468c4988fcc051