Rename `ArgList::push` methods to `with` and add new `push` methods which take `&mut self`

[atornity]

Objective

The ArgList::push family of methods consume self and return a new ArgList which means they can't be used with &mut ArgList references.

fn foo(args: &mut ArgList) {
    args.push_owned(47_i32); // doesn't work :(
}

It's typical for push methods on other existing types to take &mut self.

Solution

Renamed the existing push methods to with_arg, with_ref etc and added new push methods which take &mut self.

Migration Guide

Uses of the ArgList::push methods should be replaced with the with counterpart.

old	new
push_arg	with_arg
push_ref	with_ref
push_mut	with_mut
push_owned	with_owned
push_boxed	with_boxed