Selecting text that crosses the top scroll edge could push the
floating selection menu above the viewport because only the X
position was clamped, not Y. Add getDesktopClampedY alongside the
existing X clamp in selectionMenuPosition.ts, measure the menu's
height the same way its width is measured, and re-clamp Y in
showMenu, the layout effect, and the resize handler.
Ported by hand: TextSelectionMenu.tsx changed significantly on main
(comment mode, glass surfaces, header drag-zone push-down) since this
fix was written, so main's file was kept and the fix re-applied on
top of it.
Closes#2257
Bohdan Triapitsyn
627add0dd0