widget: Change slightly the gesture cancellation policy in a same widget

widget: Change slightly the gesture cancellation policy in a same widget

Within a widget, if a gesture accepts a sequence, it would previously
cancel every other gesture that not in the same group. Change this to
only cancelling gestures that previously claimed the gesture, and let
gestures with state=NONE for that sequence remain like that.

This enables late recognition of gestures, even on the presence of
another gesture group that was more eager at claiming the gesture.

One usecase is user-defined panning gestures on scrolledwindows,
if ::capture-button-press is TRUE (eg. the default), the gesture is
claimed early in order to consume the button press, but that would
tipically make every other gesture group deny the sequence. With
this change, the pan gesture can keep state=NONE, and later claim
the sequence for itself if the panning gesture is recognized.

Also, do not propagate state=DENIED to every gesture in the widget,
that was unintended.