Possibility for onMouseClick to consume the click event, but not initiate dragging.

[p0nce]

For now:

• returning false from onMouseClick does not consume the event
• returning true from onMouseClick always initiate dragging

Need a third way that says "consume the event, but do not initiate dragging. Dragging effect is:

• lock mouse to the window
• transform onMouseMove into onMouseDrag
• delay calling onMouseExit until dragging is terminated (mouse is released)

[p0nce]

I have this in a prototype:

enum ClickOutcome
{
    ignored, // Widget did not process the click
    drag,    // Widget processed the click and started dragging
    consumed // Widget consumed the click.
}

but I think returning bool + a startDragging call is a bit better?

[p0nce]

Perhaps separate "initiate/abandon mouse dragging" from "respond on a click"

[p0nce]

Done in v13