Skip adding degenerate faces in textToModel

[davepagurek]

Addresses one case of #4791

While this warning generally indicates a problem with the user's vertex input, we also get this warning sometimes when calling font.textToModel(). In this case, there's nothing the user can do about it, so the warning is distracting and misleading. While this doesn't fully deal with that warning happening more often than it should, this resolves the textToModel case.

(EDIT: maybe this actually does fully resolve the original issue? Looking back at it, the original sketch in question was also triangulating a font. Now that we have a way to do this internally that doesn't create warnings, the rest is likely user input issues.)

Changes:

• Adds a _validateFaces flag which, when set to true, checks if faces are valid before adding them to a p5.Geometry
  • Currently this is only used for internal triangulated shapes, so the checking is not yet done in TRIANGLE_STRIP mode.
• Turns on this flag while generating models of text, as this uses triangulation and may get a warning after calling computeNormals otherwise.

Before:

After:

Live: https://editor.p5js.org/davepagurek/sketches/zOmI5K3__ (try toggling the script tag to 2.0.3 in index.html)

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated

[perminder-17]

This looks good to me :)