Implement more precise and reliable p/items-at-point

It doesn't require "raw-point" anymore (i.e. clientX/clientY of the
event), but can figure out if the point is over the item's text just
from regular "point" (in coords).

It allows to highlight items more precisely, now there is no need to
pass "raw-point" into controller, and it simplifies further
implementation of z-indexes