Add 'pick_on_bounds' property to symbolwidgets for clicking intricate symbols

[DenSinH]

We have some intricate symbols with transparency, but clicking them can be quite annoying, as the mouse might hover over a small transparent region of the image, which makes it not register the hover state / makes it unclickable. We added a property named after the corresponding JavaFX ImageView property "pick on bounds", which makes the entire image bounds clickable, regardless of transparency. For backwards compatibility, it is false by default.

[kasemir]

Our site doesn't rely on clickable symbols, in fact I'd discourage that (https://github.com/ControlSystemStudio/phoebus/wiki/Display-Builder-Compatibility#actions-action-buttons).

But if you're stuck with displays full of transparent clickable symbols, this is what you'll have to do, short of updating all symbols to have for example a faint gray background ... as we had to do with the CSS icon because at least on Mac OS X it had the same problem: Click on the "C" icon in the "Doc" and nothing happens because it's mostly transparent...

Still, do we really need a new property for this, or can we simply turn this into a one-line change, making all symbols always fully clickable?

imageView.setPickOnBounds(true);

[DenSinH]

Fine by me, I figured we would do it this way just to not break the "default" behavior for other users. I'm sure you might not be too eager to just add properties for all such things 😅