Use a separate syntax-ppss cache for narrowed buffers

Use a separate syntax-ppss cache for narrowed buffers

* lisp/emacs-lisp/syntax.el (syntax-ppss-wide):
New variable, to contain the data from `syntax-ppss-last' and
`syntax-ppss-cache'.
(syntax-ppss-cache, syntax-ppss-last): Remove.
(syntax-ppss-narrow, syntax-ppss-narrow-start): New variables.
(syntax-ppss-flush-cache): Flush both caches.
(syntax-ppss--data): Return the appropriate last result and
buffer cache for the current restriction.
(syntax-ppss, syntax-ppss-debug): Use it (bug#22983).