* lisp/progmodes/ruby-mode.el (ruby-expression-expansion-re): Allow to

* lisp/progmodes/ruby-mode.el (ruby-expression-expansion-re): Allow to
start at point, so that expansion starting right after opening
slash in a regexp is recognized.
(ruby-syntax-before-regexp-re): New defvar, extracted from
ruby-syntax-propertize-function.  Since the value of this regexp
is looked up at runtime now, we should be able to turn
`ruby-syntax-methods-before-regexp' into a defcustom later.
(ruby-syntax-propertize-function): Split regexp matching into two
parts, for opening and closing slashes.  That allows us to skip
over string interpolations and support multiline regexps.
Don't call `ruby-syntax-propertize-expansions', instead use another rule
for them, which calls `ruby-syntax-propertize-expansion'.
(ruby-syntax-propertize-expansions): Move `remove-text-properties'
call to `ruby-syntax-propertize-function'.
(ruby-syntax-propertize-expansion): Extracted from
`ruby-syntax-propertize-expansions'.  Handles one expansion.
(ruby-syntax-propertize-heredoc): Explicitly call
`ruby-syntax-propertize-expansions'.
(ruby-syntax-propertize-percent-literal): Leave point right after
the percent symbol, so that the expression expansion rule can
propertize the contents.

* test/automated/ruby-mode-tests.el (ruby-heredoc-highlights-interpolations)
(ruby-regexp-skips-over-interpolation)
(ruby-regexp-continues-till-end-when-unclosed)
(ruby-regexp-can-be-multiline)
(ruby-interpolation-inside-percent-literal): New tests.

* test/indent/ruby.rb: Add multiline regexp example.