Fix registering touch screen edge actions after the screen edge has been reserved
After the screen edge is reserved, the touch screen gestures will be registered or unregistered when the Edge::activatesForTouchGesture() signal is emitted.
On the other hand, Edge::reserveTouch() lacks code to emit that signal, which results in touch screen gesture not working if the same screen edge is reserved both for pointer and touch input.
(cherry picked from commit 6be238e6)