Fix floating icon view positioning when in multiwindow mode.

The rect we passed in was in screen space to match the window, but needs to be
be local to launcher.

Also updated code/comments to make it more readable.

Note that the bounds of the targets being off is a separate issue b/153581126

Bug: 135195169
Change-Id: I4a8c0aa2f504bdf69342a927725cd440fb324a36