Reduce the use of trailing commas

[devoncarew]

This package was updated to use trailing commas for generated parameter and expression lists in order to address (substantial) dart format slowdowns when formatting some larger generated files.

It would be nice to dial back the use of trailing commas a bit so that shorter methods (with <= three parameters?) are generated without trailing commas.

dart-archive/code_builder#390 was one such attempt at reducing the use of trailing commas.