Indent broken arrow function bodies as an N+1th arg

Indent broken arrow function bodies as an N+1th arg

* lisp/progmodes/js.el (js--line-terminating-arrow-re): Revise regexp
for use with re-search-backward.
(js--looking-at-broken-arrow-function-p): Remove.
(js--broken-arrow-terminates-line-p): Replacement for
js--looking-at-broken-arrow-function-p.  Don’t consider whether an
arrow appears at point (in an arglist); instead, just look for an
arrow that terminates the line.
(js--proper-indentation): Use js--broken-arrow-terminates-line-p.

* test/manual/indent/js.js: Add test for a broken arrow as an N+1th
arg.