Handle making a p5.Texture out of the main canvas

[davepagurek]

Resolves #5814

Previously, if you passed the main canvas into a shader uniform, it would initially work, but would break on updates. This is because it was getting handled as an p5 HTML element rather than something p5.Graphics-like.

Changes:

• Adds handling for a p5.Renderer
• Adds tests to make sure resizes are handled for image, p5.Graphics, and p5.Renderer sources

PR Checklist

• npm run lint passes
• [Inline documentation] is included / updated
• [Unit tests] are included / updated