Port indentation code from js2-mode to js-mode

Port indentation code from js2-mode to js-mode

* lisp/progmodes/js.el (js-auto-indent-flag): Remove, was unused.
(js-switch-indent-offset): New option.
(js--proper-indentation): Use it.  And handle the case when
"default" is actually a key in an object literal.
(js--same-line): New function.
(js--multi-line-declaration-indentation): Use it.
(js--indent-in-array-comp, js--array-comp-indentation): New
functions.
(js--proper-indentation): Use them, to handle array comprehension
continuations.