Mousemove while drag-selecting downwards slows down scrolling of grid

[DataGridXL]

When mouse-drag selecting downwards (mouse outside of grid), edge detection is activated. Only when mouse stays still the scrolling remains in a solid tempo.

When mouse moves during this drag action, even if mouse movement/coordinates should not affect grid scroll speed (eg. mouse only moves horizontally, which should not affect vertical scroll speed), grid scrolling slows down considerably.

[DataGridXL]

v3 does edge detection based on request animation frame, not based on timeouts. Let's make sure to implement a new approach that does not encounter this issue.