[PATCH 3/3] user32: Send WM_CANCELMODE to the current capture window after initializing a modal dialog.

[Zebediah Figura (she/her)]

For what it's worth, as far as I can tell this really is specific to
modal dialogs. Modeless dialogs don't trigger WM_CANCELMODE. Neither
could I trigger it by emulating our modal dialog code with normal
windows (i.e. disable the owner, create an owned popup, show it). I
didn't include tests for the latter, but can rework my manual test
kludge into something automatable if it's helpful.

Also, it really is SendMessage(WM_CANCELMODE) and not just
ReleaseCapture(). Overriding the message prevents capture from ever
being released. I can add tests for that too if it's helpful.