Use ICU case conversion/transliterator for case conversion behind a flag

test/intl/intl.status

Index: test/intl/intl.status
diff --git a/test/intl/intl.status b/test/intl/intl.status
index 5ce4bf52afc2c6996ba2e0ffcc7f47d4d797cd99..bfea0bb2a59b1d7577490e0031632fcfb9a5d743 100644
--- a/test/intl/intl.status
+++ b/test/intl/intl.status
@@ -35,5 +35,9 @@
   'date-format/parse-mdyhms': [FAIL],
   'number-format/parse-decimal': [FAIL],
   'number-format/parse-percent': [FAIL],
+
+  # BUG(v8:4476, v8:4477). toLowerCase and toUpperCase fixes
+  # are behind a flag, --icu_case_mapping.
+  #'general/case-mapping': [FAIL],
 }],  # ALWAYS
 ]