Indent arrows’ expression bodies like function bodies (Bug#25904)

Indent arrows’ expression bodies like function bodies (Bug#25904)

* lisp/progmodes/js.el (js--continued-expression-p): Don’t confuse
‘=>’ for a ‘>’ operator.
(js--line-terminating-arrow-re): New variable.
(js--looking-at-broken-arrow-function-p): New function.
(js--proper-indentation): Don’t align arrow functions’ expression
bodies starting on new lines like list continuations, instead align
them like function bodies (js-indent-align-list-continuation need not
be nil).

* test/manual/indent/js.js: Add test for Bug#25904.

Co-authored-by: Felipe Ochoa <felipe@fov.space>