fix(accessibility): add bezier and spline to accessible output

[Kunal241207]

Resolves #9236

Changes:

• Add accessibility output support for bezier() and spline().
• Calculate approximate position and area for curves in textOutput() and gridOutput().
• Respect spline ends and tightness properties when generating accessibility output.
• Use the fill color and calculated area for filled curves, and stroke color with zero area for stroked curves.
• Calculate the centroid of the filled curve region for a more accurate position.
• Add unit tests covering bezier/spline output, spline ends and tightness, and noFill() behavior.

Screenshots of the change:
Not applicable — this change affects generated accessibility output rather than the visual canvas.

PR Checklist

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