Fix: restrict setHeading() to 2D vectors and add friendly error for others

[reshma045]

Resolves #8215

Changes:

This PR updates the p5.Vector.setHeading() method to support only 2D vectors in alignment with the proposed 2.x design.

• Added a dimension check in setHeading():
• If the vector’s z component is nonzero (i.e., not 2D), the method now emits a clear p5._friendlyError() explaining that setHeading() is 2D-only in p5.js 2.x.
• For 2D vectors (z === 0), heading behavior remains the same, preserving magnitude and rotating in the xy-plane.
• Keeps compatibility with existing sketches that use setHeading() on true 2D vectors.

PR Checklist

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

[perminder-17]

Really sorry for the delay in the review @reshma045 , I was out of my city.

[perminder-17]

I think this block of code is mostly redundant. When m === 0 we had this.x = m * Math.cos(a) which comes out to be this.x = 0 * Math.cos(a) which is this.x = 0, so we can remove this block and revert that change.

[perminder-17]

Do you think, this condition is not correct, since the z component of the vector can be zero and it could still be a 3-d vector. Maybe you need to replace this.z !== 0 with this.z !== undefined.

[perminder-17]

Also, one more thought. Since setHeading() is logically meaningful only for 2d vectors, so do you think we need to check this.y === undefined as well?

[reshma045]

@perminder-17 Thanks for the review, and no worries about the delay.

Updates made:

1. Removed the m === 0 special-case block
   As you pointed out, it was redundant since m * cos(a) and m * sin(a) already resolve to 0 when m === 0.
2. Corrected the dimensionality check
   Replaced the this.z !== 0 condition with a proper dimensional check. setHeading() now explicitly guards against non-2D vectors by checking: this.y === undefined (not a 2D vector), or this.z !== undefined (3D or higher)

Please let me know if you’d prefer any other modifications.