constraints: Allow resize of windows moved above screen

If the titlebar of a window has been moved above the screen by a user via an unconstrained move, then any constrained user resize following this move will cause the window to jump below the top of the screen or cause other glitchy behavior.

This commit removes the constraint that the titlebar of a window must be below the top of the screen for any resize that is both (1) triggered by a user and (2) is a resize that affects only the left, right, or bottom edges of the window. This allows users to move a window partially above the screen and then resize the window to be wider or resize the bottom edge of the window to make it taller or shorter.

Closes: #1206 (closed)