glarea: Add support for explicit synchronization
For glarea widgets, there is a need to determine when the previously submitted buffer has been consumed by the windowing system. This is particularly important if the buffer is backed up by a texture that is associated with a dma-buf.
Upstream Wayland/Weston supports explicit sync protocol that makes it possible to make such a determination. Most of the code added in this MR is based on this Weston client: https://cgit.freedesktop.org/wayland/weston/tree/clients/simple-dmabuf-egl.c