display: Don't special-case is_wayland grabs when we sync_input_focus

meta_wayland_seat_repick already detects this case and reacts
accordingly.
display: Rename grab_op_is_wayland to grab_op_should_block_wayland

The idea here is that while we take a WM-side grab, like a compositor
grab or a resizing grab, we need to remove the focus from the Wayland
client.

We make a special exception for CLICKING operations, because these
are really an internal state machine while you're pressing on a button
inside a frame, and in this case, we need to not kill the focus.
display: Rewrite grab_op_should_block_wayland to be a tiny bit clearer
display: Wayland client grabs should not block Wayland input focus

This fixes menu issues with GTK+.
pointer: Don't use default_grab_focus in popup grabs

default_grab_focus tries to add implicit grab semantics where
focus won't take effect if there's a pointer button down. This
is not what we want for popup grabs at all, as it's perfectly
valid to want to drag on a menu while there's a button down.