ecore_wl2_subsurface: support foreign shell

ecore_wl2_subsurface: support foreign shell

Please refer to following enlightenment commit message,
for more well defined information about the foreign shell.

  commit b213f873bc279d7957d407aec5f6157713bbf0b2
  Author: Seunghun Lee <shiin.lee@samsung.com>
  Date:   Fri Apr 9 14:41:03 2021 +0900

    Support wtz-foreign protocol
    This is an initial commit to support wtz-foreign protocol.

    This is to support out-of-process video playing surface.
    wtz-foreign protocol is to enable one client to share its resources to
    another client.
    The client which exported a reference of foreign shell then can change
    attributes - such as size, orientation, and map state - of foreign shell.
    So, the client which import a foreign shell can draw its contents onto a
    surface without concerning about attributes such as size like as
    mentioned.

    The e_foreign contains implementation of wtz_exporter and wtz_importer.
    And e_foreign_shell contains implementation of wtz_exported_shell and
    wtz_foreign_shell.

Change-Id: Ie9b5bd5cea33263673f9d551b0486f08f84cb4a7