Merge stuff from upsteam ruby-mode, part 1.

Merge stuff from upsteam ruby-mode, part 1.
* lisp/progmodes/ruby-mode.el (ruby-mode-map): Remove deprecated
binding (use `M-;' instead).
(ruby-expr-beg, ruby-parse-partial): ?, _, and : are symbol
constituents, ! is not (but kinda should be).
(ruby-singleton-class-p): New function.
(ruby-expr-beg, ruby-in-here-doc-p)
(ruby-syntax-propertize-heredoc): Use it.
(ruby-syntax-propertize-function): Adjust for changes in
`ruby-syntax-propertize-heredoc'.

* test/automated/ruby-mode-tests.el (ruby-should-indent)
(ruby-assert-state): New functions.
Add new tests.

Fixes: debbugs:12169