egl/wayland: Flush after blitting to linear copy

We need to flush after blitting to the linear copy, or the Wayland
compositor may not see the correct linear buffer contents.

v2:
* Keep blitImage call in the same place (Daniel Stone)
* Add second flush for the blit to linear copy

Fixes: 58f90fd03f ("egl/wayland: fix glthread crashes")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9816
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27718>
(cherry picked from commit 7a6836611e39cf00c32b6e189ca7eb2f370d68fe)

.pick_status.json

@@ -1114,7 +1114,7 @@
         "description": "egl/wayland: Flush after blitting to linear copy",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "58f90fd03f4aaf2ee19010e9cbd9cee2deda9711",
         "notes": null

src/egl/drivers/dri2/platform_wayland.c

@@ -1643,6 +1643,12 @@ dri2_wl_swap_buffers_with_damage(_EGLDisplay *disp, _EGLSurface *draw,
          dri2_surf->current->dri_image, 0, 0, dri2_surf->base.Width,
          dri2_surf->base.Height, 0, 0, dri2_surf->base.Width,
          dri2_surf->base.Height, 0);
+
+      if (dri2_dpy->flush) {
+         __DRIdrawable *dri_drawable = dri2_dpy->vtbl->get_dri_drawable(draw);
+
+         dri2_dpy->flush->flush(dri_drawable);
+      }
    }
 
    wl_surface_commit(dri2_surf->wl_surface_wrapper);