[Moomo]

On macOS 26, after switching away from a native fullscreen Space and back,
clicking near the top of the window can deliver a bogus motion event between
otherwise correct press/release positions. This makes click handlers interpret
a stationary click as a drag and cancel it.

A captured downstream sequence on macOS 26.7.1 was:

• press at (142.6, 27.1)
• motion to (-668.4, -1052.9), sometimes followed by an exit
• release at (142.6, 27.1)

For motion/drag callbacks in native fullscreen windows on macOS 26+, query the
live pointer position through NSWindow and convert it to the receiving
NSView. Button, wheel and other gesture callbacks retain their event-time
coordinates. During a held gesture, suppress an exit only while the live pointer
is actually inside the view; genuine outside movement and releases remain valid.
Windowed mode and older macOS versions retain the existing path.

This follows the scoped workaround described in
SDL's implementation.
Using Cocoa's window/view conversion avoids manually subtracting display origins.
There is a tradeoff: affected motion uses the position at dispatch time rather
than the historical event position.

Validation:

• cargo test -p winit-appkit --lib: 8 passed on macOS 26.7.1.
• cargo clippy -p winit-appkit --all-targets -- -D warnings: passed.
• The equivalent fix was backported to 0.30.13 in an egui application; the user
  confirmed that repeated header clicks work after restarting with the fix.
• Downstream event-sequence tests cover the captured click failure, corrected
  stationary clicks, genuine outside drags and moving out and back before release.
• Interactive confirmation is for the 0.30.13 backport, not a separate interactive
  run of this master-branch port. Multiple-display/scale combinations and other
  macOS versions have not been exhaustively tested.
• Nightly rustfmt is not installed locally. Stable rustfmt was used on the edited
  code, with unrelated formatting changes removed; nightly formatting may need
  to be applied by CI/maintainers.

Checklist:

• Tested on the changed platform (see scope above)
• Added a changelog entry
• Documented the platform-specific behavior in code and this description
• No new API/example required