Make reserved word assignment regex work better with function calls

[davepagurek]

Resolves https://github.com/processing/p5.js/issues/5734

Changes:

• Made the assignment statement regex a little bigger to handle more edge cases:
  • Instead of splitting on all commas, it uses a regex to parse the whole list of assignments
  • It will now correctly parse single-level function calls and ignore them
  • It will stop parsing after anything it doesn't match so that it doesn't introduce new false positives
  • It still uses regexes instead of writing a simple recursive parser to avoid complexity/bugs
• Added tests to make sure function parameters on right hand sides of assignments are ignored

PR Checklist

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

[limzykenneth]

Pretty complex regex there that took some time to wrap my head around. If we didn't miss anything obvious it should be good enough for now. Thanks!

[Qianqianye]

Thanks @davepagurek and @limzykenneth ✨