[win] Fix windows never receiving a mouseup event after moving/resizing

[ckaiser]

Fixes #aseprite/5449 and potentially a few other edge cases and event weirdness. Inspired by the solution used by Qt.

[dacap]

I wasn't able to test this yet, but I'm not sure about this solution, probably we could generate a WindowLeave and then a WindowEnter event? similar to aseprite/aseprite@c31aadae9 I need to give a try on Windows yet to check the bug it fixes first.

[ckaiser]

It feels more like something that should be handled at the LAF level transparently, since it's a platform quirk combined with a quirk of how we handle mouse input (storing the keys based on events instead of providing ways to query the mouse), but I'm open to suggestions on a different way to go about it

[dacap]

Just testing on Linux. Pressing all mouse buttons (left/middle/right) on the left window, then Alt+tab to the right window, and release those buttons, laf sends a mouse up for each button to the left window and the capture is lost:

2026-05-28.08-23-29.mp4

I'll test this on Windows later, but I think with this PR we can match the Linux behavior.