Previously, a region that used size snapping could be dragged to a
snapped size (say 3 times a column width), but then would be clamped to
an unsnapped size (say 2.7 times a column width) to make it fit the
available space.
Instead clamp the size before snapping, so that snapping respects the
available width/height (resulting in 2 times a column width for
example). Put differently, the region will not be made taller if there's
not enough space to fit the region up to the next snapping point.
Implemented as part of #104831.
Pull Request: https://projects.blender.org/blender/blender/pulls/109027
248b322896