[Policy] Allow better variable names like $snake_case (or possibly $camelCase)

I use moodle coding style when developing plugins, but the variable naming section could improve a little. Not allowing any type of word separation (snake_case or camelCase) makes the names hard to read.

While we should avoid unnecesary long variable names, by far I see variables with names shorter than it should. I will not try to arguee on why variable names should be descriptive enough.

My suggestion is to adopt $snake_case in the same way as method names. I am not asking to refactor the whole moodle, but allow it for newer code and plugin developers.

There is no code change needed for that, only a Moodle HQ reflection and opinion on the topic (although we may need to adapt a few of our code checking tools).

More information: https://docs.moodle.org/dev/Coding_style#Variables