Begin using Pointer Handlers in Controls

There is a lot of custom event handling (and some filtering) going on in the templates. Since 5.10 or so, we've been hoping to prove the value of pointer handlers by using them in Controls. (And one reason for putting it off this long has been fear of the overhead from constructing extra QObjects.)

Maybe it would be easier to start with some relatively-isolated component like SwipeDelegate.

MenuItem might particularly benefit from using TapHandler, if we continue with https://codereview.qt-project.org/c/qt/qtdeclarative/+/557648 : it should be able to detect a release without having to see the press first. But that inherits QQuickAbstractButton; so if we start there, it will probably affect a lot of controls.

Since Controls has independent public API, presumably the templates will be constructing them in C++, connecting signals and so on behind the scenes.