merge revision(s) 8aecc909,2f6cc15c: [Backport #15965]

	Hoisted out WIDE_ENCODINGS


	Fixed String#grapheme_clusters with wide encodings

	* string.c (get_reg_grapheme_cluster): make regexp from properly
	  encoded sources fro wide-char encodings.  [Bug #15965]

	* regparse.c (node_extended_grapheme_cluster): suppress false
	  duplicated range warning for the time being.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67741 b2dd03c8-39d4-4d8f-98ff-823fe69b080e