Remove reference to p5 instance in p5.Vector objects

[limzykenneth]

Resolves #5367

Changes:
Change constructor signature called by createVector() of p5.Vector to accept _fromRadians and _toRadians functions as first two arguments with their this value bound to the original p5 instance. This isn't changing any documented public signature so shouldn't be a breaking change.

As a result, test now pass on both node 14 and node 16 because there is no longer cyclic references in p5.Vector.

PR Checklist

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