Curved text: experimental arbitrary path and Bezier text

[rowland]

Summary

Prototype arbitrary path-following text without overcommitting the stable API.

Scope

• Add an internal or explicitly experimental path-text entry point for cubic Bezier paths and piecewise paths.
• Support paths derived from control points, not full SVG text-on-path semantics.
• Define first-version constraints:
  • no glyph warping
  • no support guarantee for cusps or self-intersections
  • callers must provide a smooth enough path for readable output
• Capture shortcomings discovered here as follow-up issues instead of broadening scope midstream.

Acceptance Criteria

• Add prototype tests with simple cubic paths and multi-segment paths.
• Mark the API and docs as experimental.
• Document known limitations, especially around tight curvature and spacing artifacts.