Update docs for setHeading

[babaissarkar]

Resolves #472

Adds JavaDoc for PVector#setHeading() and the associated keywords.txt entry, generated using the instruction at https://github.com/processing/processing-website?tab=readme-ov-file#keywordstxt. This allows the Syntax Highlighting and Open Content Reference context menu item to work.

(Note: Open Content Reference will open missing page until processing/processing-website#621 is merged and properly deployed.)

(Note 2: Also updates the documentation for PVector#heading() to be more explanatory, inspired by https://p5js.org/reference/p5.Vector/heading, so that JSON might also require regeneration. (Done) )

Adds more missing keywords to the keywords.txt file. (Generated via keywords.txt update routine)

[babaissarkar]

While running the update routine for keywords.txt I came across some API functions that were missing from it, so I added them in 7d691d8. I've checked that the online reference pages for those functions already exist, they were just missing syntax highlight/content reference support.

[SableRaf]

@all-contributors please add @babaissarkar for code and documentation

[allcontributors]

@SableRaf

I've put up a pull request to add @babaissarkar! 🎉

[SableRaf]

Thanks @babaissarkar for the great work and for your patience! Your change will go out in the next release of Processing 4.4.5.

We'd be happy to see you contribute further. Feel free to look at other open issues and/or join the Processing Community Discord. And let me know if you need any pointers 💙