spinbutton: increase/decrease value on upwards/downwards touch swipes

This is somewhat analogous to scroll events on pointer devices, the
greater the velocity, the faster the spinbutton spins.
enums: Document GtkPropagationPhase
Remove GtkPressAndHold

This is replaced by GtkGestureLongPress, and all its callers have
been updated to use the replacement.
enums: Add missing docs to controller/gesture enums
eventcontroller: Add missing documentation
gesture: Add missing documentation
gesturesingle: Add missing documentation
multipress: Add missing documentation
longpress: Add missing documentation
drag: Add missing documentation
swipe: Add missing documentation
rotate: Add missing documentation
zoom: Add missing documentation
pan: Add missing documentation
docs: Add missing controller/gesture docs
eventcontroller: doc fixes
gesture: doc fixes
drag: doc fixes
longpress: doc fixes
multipress: doc fixes