Revisit "Handle clicks in indentation area"

Revisit "Handle clicks in indentation area"

Check (x, y) is inside background area.  If yes, continue processing
and clamp the coordinates into cell area.  This way we will properly
handle getting a cell (which is only used for setting the focus cell)
for clicks in the indentation area (in LTR and RTL mode) and clicks
in the focus rectangle area in case focus-line-width is large.