Improve responsiveness of triangular filter
The responsiveness of the filter is improved by adding two new metrics to the filter logic: - Firstly, the direction of the cursor movement is considered. If (in the default configuration) the filter is currently active and the user moves the cursor to the left (away from the content area), the filter stops intercepting the movement events. This results in a noticeable improvement in responsiveness without compromise the objective of the filter. - Secondly, a velocity metric (as already brought up in BUG 438950) is added. This ensures that a very slow movement of the cursor results in disabling the triangular filter. This, also, improves the the feeling of responsiveness significantly. Still, there is a need for the timer in the filter, as when the cursor has stopped its movement completely, it will no longer send HoverMove events to the filter, thus it wouldn't be possible to detect a complete stop of the cursor.
(cherry picked from commit 6c18efd1)