(sgml--syntax-propertize-ppss):New variable and function.
(sgml-syntax-propertize-rules): Use it.
Don't ignore quotes not followed by a matching quote or a '>' or '<'.
(sgml-syntax-propertize): Set up sgml--syntax-propertize-ppss.
* test/lisp/textmodes/sgml-mode-tests.el (sgml-tests--quotes-syntax):
Add test for lone '>'.