Add eslint rule to warn about the comma operator.  Comma operators in our code are almost always mistakes stemming from bad or incomplete SC conversion.

Made unused vars ignore arguments, since there's a lot of false positives when the variables are there as documentation on callbacks or for protected virtual overrides in classes.

This reverts merge request !4538

Allow space before function parens for anonymous functions and async
lambdas (rationale: a) we put space between 'function' and its name, in
these cases the name is simply not present; b) lambdas look this way).