OnMouseMove event dispatcher.
procedure MouseMove(Shift: TShiftState; X: Integer; Y: Integer); virtual;
Override the protected MouseMove method to provide other responses in addition to calling the OnMouseMove event handler when the user moves the mouse.
A control calls MouseMove in response to any of the Windows mouse-move messages (WM_MOUSEMOVE), decoding the message parameters into the shift-key state and position, which it passes in the Shift, X, and Y parameters, respectively.
As the mouse cursor moves across a control, this method is called repeatedly. Each time it is called, it is with the new coordinates that reflect the continuous path of the mouse cursor across the screen real estate covered by the control's visual representation
X,Y coordinates are relative to client origin of the root pane FRootPane.