Return each X11 monitor so games can choose where to open

[relh]

Games need each monitor’s position and size to place a window on the chosen display. The old change returned one rectangle covering the desktop, so it could not distinguish two monitors.

Use RandR 1.5 to return active monitor rectangles and their primary flags. This requires libXrandr and a server supporting RandR 1.5. The example prints the result on every supported platform, including the browser.

Validation: on a real Xvfb server configured with two 800 by 600 monitor regions, the old code returned one 1600 by 600 rectangle. The new test returns two distinct rectangles. A rendered check used those bounds to place two colored windows, one inside each region. This is virtual-monitor runtime evidence, not a physical multi-monitor or hot-plug test. The regression runs in the existing Linux CI job.

Updated to current upstream master. Addresses the existing request to return every screen.

The implementation checks passed on Linux, macOS, and Windows. The final change only moves this test step beside the screen example so it combines with the pending VSync PR; its final run has also passed on all three platforms. The runtime limits above still apply.

[treeform]

just X11

[relh]

[Codex, acting on behalf of relh]

Reviewed 5db2a77. The screen-enumeration concern in André's existing inline review remains unresolved: defaultScreen still produces one aggregate X11 screen rather than all attached monitors. The example's Linux guard has been removed, so that separate comment has been addressed. No additional distinct finding. I reviewed the current diff and existing thread; I did not run a multi-monitor X11 session.