search: add FloatConstraint

Change-Id: Ic367e87cb239258a76a99c9d07f0956d67e242ea
search: add is:portrait, is:landscape, and is:pano

Also support Width and Height constraints on raw search (not yet
exposed to the expression syntax, but will be like width:<640 or
height:100-200 probably)

Change-Id: I082e3d27b5ef5c238a8e65a6b836943d9f9ff8a6