Improve PHPDoc Types

[james-cnz]

I've run a basic PHPDoc type checker over the code, and tidied up a few things. I think it's probably good for moodle-cs to set a good example.

Note: I know the PHPCS Sniff function process() specifies its return type as void|int, but AFAIK, void is a stand-alone type, and int|null is the correct type.

[jrchamp]

None of the process() methods that I looked at had a return that was anything other than void (i.e. return;). Where are you seeing int returns? Also, if nullable int were the correct return value, I'd lean towards ?int over int|null because - to me - it implies "sometimes you get an integer" as opposed to "sometimes you get an integer which means A and sometimes you get null which means B".

I hope that helps! I'm sure others will have more comprehensive feedback.

[james-cnz]

Yeah, I don't think any of the process methods in moodle-cs return int. It would also be valid to specify the return type as just null. It's in the base method, though, and I didn't think there was any point narrowing it.
https://github.com/squizlabs/PHP_CodeSniffer/blob/master/src/Sniffs/Sniff.php
The return statements should probably say return null; for good style, but PHP defaults to null if trying to read the return value of a function when none was provided.
I used int|null because it conforms to PSR-5, which I've been told the Moodle code base uses, so I've leaned into this style where possible. Maybe it's not appropriate for moodle-cs, though.