fix(wayland): Hand the pointer to an X11 menu only once it has a surface
While an X11 menu is open the pointer is the menu's, but the menu was
taken as the pointer's focus as soon as it mapped, before Xwayland gave
its window a surface, so no enter reached Xwayland and it dropped every
motion after it until the menu closed: a context menu froze the pointer
and only Escape gave it back. A menu with no surface yet is no longer
the pointer's, and one that has one is entered at its surface's origin
rather than inside the shadow its toolkit draws, which put every point
in the menu off by that inset.