Dragging a sash with alt to the far side of the window causes the other sash to move

[RMacfarlane]

Testing #44127

Steps:

• Go into centered layout mode using the command Toggle Centered Layout
• Hold alt and drag a sash far to the side, beyond the window

Expected: Once the sash has reached the end of the window, continuing to drag will do nothing
Actual: The sash on the other side begins to move outward

[isidorn]

Pushed some code which brings back this behavior.
Reopening

[bpasero]

@isidorn maybe this should be looked at when doing the widget for #50936

[isidorn]

@bpasero makes sense, let me assign this to June

[isidorn]

This is fixed in latest with the new split view math - yeee