* lisp/progmodes/ruby-mode.el: Improve percent literals.

* lisp/progmodes/ruby-mode.el: Improve percent literals.
(ruby-percent-literal-beg-re): New constant.
(ruby-syntax-general-delimiters-goto-beg): Rename to
`ruby-syntax-enclosing-percent-literal', improve literal type check.
(ruby-syntax-propertize-general-delimiters): Rename to
`ruby-syntax-propertize-percent-literal', it's a shorter and more
popular term.  Adjust comments everywhere.
(ruby-syntax-propertize-percent-literal): Only propertize when not
inside a simple string or comment.  When the literal is unclosed,
leave the text after it unpropertized.

Fixes: debbugs:6286