SF: Add support for boundless layers 2/2

Size is currently used to bound a layer and its child layers. There are
scenarios where we do not want to restrict a layer or its children to any
specific size but have it expand to fill its parent bounds (in the case of a
color layer) or use the size of its buffer. Currently this is achived by providing
a large enough size so that the layer or its children do not get cropped incorrectly.

To fix this, we start by modifying computeBounds and computeScreenBounds
to ignore a layer's size. We calculate the bounds by using the layer's buffer size
and/or crop. In WM, we set the layer's crop property if we want to crop the layer
or child layer to a particular bounds.

Bug: 114413815
Test: go/wm-smoke
Change-Id: I633669876ae434d996532c4d808badabfe3f6787