[p5.strands] Add full support for using filter shaders on 2d sketches.

[nbogie]

Increasing access

1. Many people who only know 2d sketches (not 3d) should be able to write and consume filter shaders with strands (or glsl) for those 2d sketches.

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
• Internationalization
• Friendly errors
• Other (specify if possible)

Feature enhancement details

Add as much of the functionality as possible.

TODO: Add a list of the functionality here which we find is not available when we try to buildFilterShader when the main context is 2d not 3d.

Missing functionality (placeholder):

• filterColor is not defined: example
• noise() - this._renderer.getNoiseShaderSnippet is not a function: example