* lisp/nxml/nxml-mode.el: Use lexical-binding and syntax-propertize.

* lisp/nxml/nxml-mode.el: Use lexical-binding and syntax-propertize.
(font-lock-beg, font-lock-end): Move before first use.
(nxml-mode): Use syntax-propertize-function.
(nxml-after-change, nxml-after-change1): Adjust accordingly.
(nxml-extend-after-change-region): Remove.
* lisp/nxml/nxml-ns.el: Use lexical-binding.
(nxml-ns-save): Use `declare'.
(nxml-ns-prefixes-for): Avoid add-to-list.
* lisp/nxml/nxml-util.el: Use lexical-binding.
(nxml-with-degradation-on-error, nxml-with-invisible-motion):
Use `declare'.
* lisp/nxml/rng-match.el: Use lexical-binding.
(rng--ipattern): Use cl-defstruct.
(rng-compute-start-tag-open-deriv, rng-compute-start-attribute-deriv)
(rng-cons-group-after, rng-subst-group-after)
(rng-subst-interleave-after, rng-apply-after, rng-compute-data-deriv):
Use closures instead of `(lambda...).
* lisp/nxml/xmltok.el: Use lexical-binding.
(xmltok-save): Use `declare'.
(xmltok-unclosed-reparse-p, xmltok-semi-closed-reparse-p): Remove.