Enable comma-dangle rule in ESLint, fix all errors.

[kdzwinel]

Closes #3304

[kdzwinel]

"always-multiline" means that trailing comma is required only if object/array spans to multiple lines

[kdzwinel]

trailing commas in imports/exports/functions aren't used in lighthouse code, so I turned them off. (function(a,b,)?? Yuck)

[patrickhulce]

it's actually pretty nice for clean diffs and easy copy paste of multi-line function arguments :) (need to wait awhile for node support to get there though)

SomethingVeryLong.SomethingVeryLong = function somethingVeryLong(
  aLongName,
  aSecondLongName,
) {
 //
};

[kdzwinel]

Right, with "always-multiline" it would make sense 👍

[brendankenny]

LGTM, though others may want eyes on.

All the places commas were added seem reasonable, even if it gets a bit ridiculous with some of those

        },
      },
    },
  ],
};

:)

[paulirish]

the conflicts will be fun, but it's worth it. :)