wayland/egl: initialize window surface size to window size

When creating a windows surface with eglCreateWindowSurface(), the
width and height returned by eglQuerySurface(EGL_{WIDTH,HEIGHT}) is
invalid until buffers are updated (like calling glClear()).

But according to EGL 1.5 spec, section 3.5.6 ("Surface Attributes"):

  "Querying EGL_WIDTH and EGL_HEIGHT returns respectively the width and
   height, in pixels, of the surface. For a window or pixmap surface,
   these values are initially equal to the width and height of the
   native window or pixmap with respect to which the surface was
   created"

This fixes dEQP-EGL.functional.color_clears.* CTS tests

v2:
- Do not modify attached_{width,height} (Daniel)
- Do not update size on resizing window (Brendan)

CC: Daniel Stone <daniel@fooishbar.org>
CC: Brendan King <brendan.king@imgtec.com>
CC: mesa-stable@lists.freedesktop.org
Tested-by: Eric Engestrom <eric@engestrom.ch>
Tested-by: Chad Versace <chadversary@chromium.org>
Reviewed-by: Chad Versace <chadversary@chromium.org>
Reviewed-by: Daniel Stone <daniels@collabora.com>
(cherry picked from commit 1fe7cbdf)