[FancyZones] Fix stuck drag state and swallowed keys when a window is destroyed mid-drag

[crutkas]

Summary

Fixes a class of "stuck drag" bugs in FancyZones where closing or destroying a window while it is being dragged leaves FancyZones in a half-dragging state — zone overlays stay on screen and subsequent keystrokes (notably number keys) are swallowed or misrouted.

What this changes

• Subscribe to and dispatch EVENT_OBJECT_DESTROY. FancyZonesApp never subscribed to the destroy event, and the consumer's WM_PRIV_WINDOWDESTROYED branch could therefore never fire. The event is now registered and routed through HandleWinHookEvent.
• Abort the drag (without snapping) when the dragged window is destroyed. On WM_PRIV_WINDOWDESTROYED, if the destroyed HWND is the one being dragged, call the new WindowMouseSnap::Abort() (tears down overlays/highlights/transparency) instead of MoveSizeEnd(), which would try to snap the now-dead HWND and corrupt zone state. Dragging state is then disabled.
• Always clear dragging state in MoveSizeEnd(), even when the snapper was already null, so the state can't get stranded.
• Require Win+Ctrl+Alt to switch layouts while dragging. Previously any digit switched layouts while dragging was true; if drag state was stuck this "stole" number keys from the focused app. This is the root-cause fix for the number-key-stealing symptom.
• Only swallow the bare Shift key during a drag, not Shift+<other> combos, so real keystrokes are no longer eaten by an in-progress drag.

Testing

• Builds Release x64 (FancyZones) clean against current main.
• Manually verified drag → close window mid-drag no longer leaves overlays up or steals number keys. (FancyZones has no unit-test harness for this path.)

This is one of a small set of related "stuck key / stuck state" hardening fixes; each stands alone.

[github-actions]

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