XWayland: Don't commit empty surfaces

Instead of attaching, damaging and then committing a new buffer as soon
as we allocate a pixmap, just attach and damage the entire buffer.  When
the buffer is changed, we'll commit the changes.

This avoids an ugly black (on SHM) flash when a window is mapped or
resized.

Signed-off-by: Daniel Stone <daniels@collabora.com>
xwayland: Also look for wlglamor
xwayland: Add wlglamor the right way

Defeated by #ifdefs.
xwayland: Don't redirect windows, leave it to the wm
Revert "Export CompositeRedirectSubwindows and CompositeUnRedirectSubwindows"

This reverts commit 15a7e62a9848f2089180c49b02887565d29bb896.

Now that we don't redirect windows on behalf of the wm, we don't need this.