v1.4.0

Commits since v1.3.2:
83da303 Release v1.4.0
5fe12c7 ci: run build-linux.yml on PRs as a required check (#722) (#35)
fe2be10 feat: open the app window on the 3D panel via XrDisplayDesktopPositionEXT (#34)
5240930 ci(linux,#30): tri-LTS build matrix (22.04/24.04/26.04) + ffmpeg 4.x compat (#33)
67bd316 chore(#691): align OpenXR loader pin to 1.1.51 + harmonize demo metadata
7592bbe linux: wire XR_EXT_xlib_window_binding — X11 handle pair from SDL, chained at session create (#30)
e93b104 linux: declare the wire-shared window-space layer struct in XrCommon.h's Linux arm (#30)
75b16e7 ci(linux): add libxcb-glx0-dev — loader includes <xcb/glx.h> once GLX support flips on (#30)
426c942 ci(linux): add libxxf86vm-dev — GL headers make OpenXR-SDK-Source configure openxr-gfxwrapper (#30)
1d94fcc linux: build-green port — build_linux.sh + run script + non-required CI (#30)