All versions of RetroArch 1.9.x repeatedly capture and refuse to release mouse cursor while fullscreen

Description

As the title says, every version of 1.9.x is affected. More info on the behavior and troubleshooting is available in the following reddit thread: https://old.reddit.com/r/RetroArch/comments/r67mfg/all_versions_of_retroarch_19x_refuse_to_release/

Expected behavior

On 1.8.x and earlier, the mouse cursor was free to roam around to other displays while RetroArch was fullscreen on its own display.

Actual behavior

Regardless of any settings or input, the mouse cursor in 1.9.x is jailed within RetroArch unless a user alt/win+tabs out, but RetroArch will re-capture the cursor on any state change (e.g., loading media, exiting media, switching resolutions).

Steps to reproduce the bug

1. Have more than one display connected
2. Launch RetroArch fullscreen on primary display
3. Attempt to interact with a window on another display

Note that if RetroArch is active on a non-primary display, the cursor's boundaries are extended to the primary display, which makes the lock in this situation only immediately obvious with three or more displays connected.

Bisect Results

I first noticed this with the release of 1.9.0 stable. The previous stable 1.8.9 is unaffected.

Environment information

• OS: Windows 10, various builds on multiple machines

Reproduce the report on Windows 10 with multiple displays, using RetroArch 1.8.9 and 1.9.x to compare fullscreen cursor behavior. Trace the fullscreen and mouse-capture handling from the 1.9.0 regression; done means the cursor can reach other displays and is not recaptured after loading media, exiting media, or changing resolution.