Fix chainable p5 instance methods returning void instead of p5

[guan404ming]

Resolves #8415

Changes:

Previously, chainable methods on the main p5 class (like background(), stroke(), fill(), translate(), etc.) were typed to return void instead of p5 in the generated TypeScript definitions. This was due to an explicit exclusion condition options.currentClass !== 'p5' in the type generation logic.

• Removes the exclusion so chainable methods on p5 return p5
• Adds special handling for global mode to use P5 (the imported type) instead of p5 (which is a namespace in global.d.ts)

Screenshots of the change:

PR Checklist

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