[WebGL] shader() | setUniform() {Examples} (Fix indent)

[hsab]

addresses #1954

• https://p5js.org/reference/#/p5/shader
• https://p5js.org/reference/#/p5.Shader/setUniform

resolves #3720
resolves #3722
resolves #3723
resolves #3724

shader() example: extends the loadShader() example to allow for toggling between 2 shaders on mouse click/press.
setUniform() example: alternative to the above, using the setUniform function to modify uniforms. Based on this comment by @stalgiag on PR #3722

[stalgiag]

Looks good! Congrats on yr first merge @hsab .

[hsab]

Haha thanks @stalgiag
I hope it's the first of many