Add a flag to indicate if the most recently created canvas is 3D

Increasing Access

This will increase access under the following rubric: "People with little or no prior experience in open source and creative coding"

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• WebGL
• Build Process
• Unit Testing
• Localization Tools
• Friendly Errors
• Other (specify if possible)

Feature request details

While trying to figure out how to easily determine whether the current canvas is in 3D mode or 2D mode for a library I'm creating, I came across this SA article:

https://stackoverflow.com/questions/60931463/programmatically-detect-rendering-mode-in-p5js

It would appear that detecting the current canvas/p5.Graphics mode is less than straightforward. Many of the 3D methods throw an exception if you try to use them on a 2D canvas, so I think it would be useful to make it somewhat easier to determine the current mode.

I propose that we add a readonly property to p5 instances and p5.Graphics instances called .is3D, paralleling the existing .isP3D property of the p5.RendererGL class. Currently, you could also look at the _renderer property to see if it is an instance of p5.Renderer2D or p5.RendererGL, but that's no simpler than the solution proposed in the aforementioned SA article.