Test the two modes of MetaAnonymousFile, MAPMODE_SHARED and
MAPMODE_PRIVATE and make sure they don't leak data to other FDs when
writing to an FD provided by `meta_anonymous_file_get_fd` even though
the data of both FDs is residing in the same chunk of memory.
We do all the reading tests using mmap instead of read() since using
read() on shared FDs is going to move the read cursor of the fd. That
means using read() once on the shared FD returned by
meta_anonymous_file_get_fd() in MAPMODE_PRIVATE breaks every subsequent
read() call.
Also test the fallback code of MetaAnonymousFile in case `memfd_create`
isn't used for the same issues.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/1012
Without 'wayland/surface-actor: Reset and sync subsurface state when
resetting' this test would fail.
This also adds a simple framework for testing lower level Wayland
semantics.
In contrast to the test-client and test-driver framework, which uses
gtk and tests mostly window management related things, this framework is
aimed to run Wayland clients made to test a particular protocol flow,
thus will likely consist of manual lower level Wayland mechanics.
A private protocol is added in order to help out clients do things they
cannot do by themself. The protocol currently only consists of a request
meant to be used for getting a callback when the actor of a given
surface is eventually destroyed. This is different from the wl_surface
being destroyed due to window destroy animations taking an arbitrary
amount of time. It'll be used by the first test added in the next
commit.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/961
