Make it possible to use HoverHandler to filter events

I'm trying to track the position of the mouse cursor regardless of what items are occupying the scene, like an event filter, but without having to resort to C++.

At first I tried using a HoverHandler on the window, but it was never hovered:

import QtQuick 2.13
import QtQuick.Controls 2.13

ApplicationWindow {
    id: window
    width: 400
    height: 400
    visible: true
    title: "hovered: " + hoverHandler.hovered

    StackView {
        anchors.fill: parent
    }

    HoverHandler {
        id: hoverHandler
        target: window.contentItem
    }
}

It seems like it is designed so that it will only get events that weren't already accepted, which makes sense. However, it would be nice if there was a way to filter hover events, similar to how PointHandler apparently allows mouse clicks to be filtered:

By being only a passive grabber, it has the ability to keep independent oversight of all movements. The passive grab cannot be stolen or overridden even when other gestures are detected and exclusive grabs occur.

If your goal is orthogonal surveillance of eventpoints, an older alternative was QObject::installEventFilter(), but that has never been a built-in QtQuick feature: it requires some C++ code, such as a QQuickItem subclass. PointHandler is more efficient than that, because only pointer events will be delivered to it, during the course of normal event delivery in QQuickWindow; whereas an event filter needs to filter all QEvents of all types, and thus sets itself up as a potential event delivery bottleneck.

One possible use case is to add this handler to a transparent Item which is on top of the rest of the scene (by having a high z value), so that when a point is freshly pressed, it will be delivered to that Item and its handlers first, providing the opportunity to take the passive grab as early as possible. Such an item (like a pane of glass over the whole UI) can be a convenient parent for other Items which visualize the kind of reactive feedback which must always be on top; and likewise it can be the parent for popups, popovers, dialogs and so on.

The docs mention MultiPointTouchArea as an alternative for some issue about macOS and trackpads, so I tried it just out of curiosity, but as expected, it didn't react to hover:

import QtQuick 2.13
import QtQuick.Controls 2.13

ApplicationWindow {
    id: window
    width: 400
    height: 400
    visible: true
    title: "x: " + point1.x

    StackView {
        anchors.fill: parent
    }

    MultiPointTouchArea {
        id: hoverHandler
        anchors.fill: parent
        touchPoints: [
            TouchPoint { id: point1 }
        ]
    }
}