Propertize operator symbol names with symbol syntax class

Propertize operator symbol names with symbol syntax class

* lisp/progmodes/ruby-mode.el (ruby-syntax-propertize):
Do it here.
(ruby-font-lock-keywords): Instead of handling them here.  Leave
highlighting them to the "normal" matcher, because now we can.
(ruby-smie--forward-token, ruby-smie--backward-token):
Likewise, don't special-case operator symbols anymore.
(ruby-smie--args-separator-p): Simplify the regexp, match operator
names with \s_.
(ruby-smie--implicit-semi-p): Handle the special cases of ? and =
at EOL the same way: check if the character has been assigned the
symbol syntax class by syntax-propertize.