Poor instanced picking performance

1. Modify the manual picking test to have "10000" instances instead of "1000".
2. Add a `DebugView` to the end of `View` to see framerate:

DebugView {
    anchors.right: parent.right
    source: viewport
}

The issue is the framerate drops from 165FPS to 27FPS without ANY interaction.

Perf report most time being spent in `QQuick3DViewport::internalPick`. I think `QQuick3DViewport` is erroneously handling hover events by default. I don't see any hover functionality builtin to `Node` or `View3D` so I'm confused why it would be raycasting.

Edit: Tweaking `QQuick3DViewport::internalPick` fixed the performance problem in my application:

const bool isHover = QQuickDeliveryAgentPrivate::isHoverEvent(event);
if (isHover)
    return false;

Not entirely sure how to make a PR, but I'd be happy to do so with the above change applied.