experimental: simplify strands tutorial (flat API, no uniforms, no arrow fns)

[nbogie]

This is an experimental PR to allow us to see how the strands tutorial might look if simplified, and what problems we might encounter in trying that.

Status:

• Uses flat API throughout
• Uses buildXShader instead of base().modify()
• Zero arrow functions (once the placeholder for millis() is removed)
• Removed definition of rand(). Use built-in noise() instead
• fix incorrectly indenting sketches (all code spans need two sacrificial leading spaces)
• All but one* use of uniform replaced with now built-in variables

* Actually, you'll see two uses of uniform remaining:

• a temporary one which serves to provide time (and keep sketches working) until millis() is implemented in strands. (added as a separate commit which can be reverted).

• uniformTexture, used to get the original image into the bloom filter. I don't have a solution for how to remove this one and keep the bloom filter.

• ISSUE: The uniform mechanism being used by uniformTexture is yet to be explained in this branch.

[ksen0]

(Minor note: millis() processing/p5.js#8530 is very close. It is aimed for 2.2.2, which is done except for that PR. So I think it is reasonable to expect millis() to be available in a patch release in the next few days.)

[nbogie]

Ta. (It looks like the build is breaking for unrelated reasons (401))

Update: at build, the site is pre-rendering pages for /sketches/<sketchid>, and to do so has to fetch some details of the sketch from the openprocessing API. These fetches were failing with 401 (possibly getting throttled by openprocessing).

Nothing to do with this PR.