Use unicorn client rect for adjacent collapsed selection

For a collapsed selection between two unicorn images, the nearest containing client rect is
actually that of the surrounding element, which can be arbitrarily wide. The unicorn's own
client rect is a better match for the cursor position.

Change-Id: I77894f24c1fee39343ce6652f999aaa9133cc511
Merge "Use unicorn client rect for adjacent collapsed selection"