unicode_normalize: UNICODE_VERSION constant

* template/unicode_norm_gen.tmpl (UnicodeNormalize): embed the
  version of Unicode data files used to generate.

* test/test_unicode_normalize.rb (TestUnicodeNormalize): use the
  embedded version to load the test data.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48357 b2dd03c8-39d4-4d8f-98ff-823fe69b080e