nightly

Warn on MIT-SHM not working on Linux X11 (#6856)

* Clarify video capture method

* fix improper level of pointer usage of xcb_generic_error_t

* add ffi of xcb_shm_query_version

* throw a warn about MIT-SHM not working

* add missing #[cfg]

* checks SHM validity on the fly, rather than cache on creation

---------

Co-authored-by: root <root@localhost>
Co-authored-by: rustdesk-fork <rustdesk@fork.com>