Detect mouse events in a Plot

[IndianBoy42]

I want to make an interactive plot, so this involves being able to click and drag the various plot elements. Currently you can use the general Response::clicked_by etc for detecting clicks/drags anywhere on the whole plot but it has a few drawbacks:

• The positions/deltas we get are in pixels, not plot coordinates.
• We would have to somehow manually check which plot elements were interacted with.

I think it would be nice if adding elements to the plot also gave something like a Response object that allows us to check interactions.
Making things automatically be draggable (especially Points, Polygons) would be nice as well.
As a long term goal, perhaps we could have projection/closest point methods as well. But first the ability to detect click/drag on Plot elements would be good

I am just starting to learn how to use egui, so apologies if I have missed an existing feature.

[IndianBoy42]

Related to #734 but more about events

[EmbersArc]

Mouse position and delta are now available in #766, feel free to give it a try.

[jbuckmccready]

@EmbersArc The mouse position functions work great! Related to this interactive/event handling plots I would like to enable/disable plot dragging to change the bounds based on where in the plot the pointer was pressed (example use case: if certain parts of the plot are editable and a control point is pressed I want to disable dragging to change bounds and instead use the drag to change the plot data). The problem is the Plot is consumed in the call to show so I am not sure how to disable dragging based on the pressed plot location. I thought maybe I could just implement dragging plot bounds separately but I couldn't find a way to edit the plot bounds programmatically.

[emilk]

I think this is closed by the PR:s above