Zigzag Shape fixes

[Logo121]

Preview

ծ‹›⧘⧙⧚⧛⦚𜺰, in max slant (‹› is not changed)

┌𜰉𜰉─𜰊𜰊
𜰊───┘𜰊

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This PR mainly tries to address the problem of mask-based composition of line segments, which has these little spikes when slanted:

The changes aren't really applicable to the guillemets, which probably needs some special treatment. (Might open a separate issue for this)

• Add a new knot interpolator sharp-corner, which simulates a "corner" biknot by calculating the intersection of the stroke edges of 2 straight lines intersecting at some reference point.
  • Assumes:
    • The knot types before/after the reference point leads to a straight line into/out of the reference (e.g. flat/curl)
    • The widths for the knots before/after are specified (the stroke information is not given otherwise)
      • The widths for the knots are assumed to be constant for the previous->reference and reference->next stroke segments.
    • The knot sink(?) is dispiro (the sink information is not given)
      • Currently the biknot is just simulated by the midpoint of the 2 edges (+ an absurd heading vector)
      • It's technically possible to arrange the knots such that the resulting knots work for both spiro-outline and dispiro, but it will further complicate the code.
• Add 2 new shared shapes: Polyline and ClosedPolyline, which returns a list of knots to draw a polyline and polygonal stroke.
  • ClosedPolyline is currently not used but is tested to be functional.
• Rewrite HZigzag and VZigzag to:
  • Include a new variant where the wave starts from the center (for 𜰉𜰊)
  • Extend the terminals so that the stroke actually reaches the edge (for 𜺰)
• Use the new functions to:
  • Rewrite ծ so that the sharp bend is a bit cleaner in both code and the resulting geometry.
  • Clean up code for 𜺰, which previously used 2 extra strokes to extend the zigzag.
  • Clean up code for 𜰉𜰊, which finally uses HZigzag VZigzag in a relatively clean way.
• Other changes:
  • Split some of the more geometric legacy symbols (including 𜺰) into its own module pictograph/geometric.ptl.
    • EDIT: I just noticed I said the same thing in 4 Currency Symbols + 2 Technical Symbols #2638, but I didn't push the game-sprite -> geometric split at that time. So this character is just gone in the current version. Whoops...

[be5invis]

Wow I always wanted to do this but never realized. Good job.