Add some support for the code-point code-unit distinction.

tests/co19/co19-runtime.status

Index: tests/co19/co19-runtime.status
diff --git a/tests/co19/co19-runtime.status b/tests/co19/co19-runtime.status
index 068e2992d3484d93430c107cb711ffbd133f6afe..5ca92f3c3fb23aab5e645719ae07b5b49b3c2742 100644
--- a/tests/co19/co19-runtime.status
+++ b/tests/co19/co19-runtime.status
@@ -192,10 +192,6 @@ LibTest/math/sin_A01_t01: Fail # TODO(vm-team): Please triage this failure.
 
 LibTest/isolate/isolate_api/port_A01_t01: Skip # Times out.
 
-LibTest/core/String/String_class_A02_t01: Fail, OK # co19 issue 284
-LibTest/core/String/charCodeAt_A01_t01: Fail, OK # co19 issue 284
-LibTest/core/String/charCodes_A01_t01: Fail, OK # co19 issue 284
-
 Language/06_Functions/1_Function_Declaration_A02_t03: Fail # issue 6058
 Language/06_Functions/1_Function_Declaration_A03_t03: Fail # issue 6058
 Language/06_Functions/2_Formal_Parameters/2_Optional_Formals_A03_t01: Fail # issue 6085
@@ -283,6 +279,12 @@ LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterClassEscape_A03_t01: F
 LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterClassEscape_A04_t01: Fail
 LibTest/core/RegExp/Pattern_semantics/firstMatch_NonEmptyClassRanges_A01_t01: Fail
 
+LibTest/core/String/String_class_A02_t01: Fail, OK # Fixed in co19 version 443
+LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterClassEscape_A06_t01: Fail, OK # Fixed in co19 version 443
+LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterClassEscape_A02_t01: Fail, OK # Fixed in co19 version 443
+LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterClassEscape_A01_t01: Fail, OK # Fixed in co19 version 443
+LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterClassEscape_A05_t01: Fail, OK # Fixed in co19 version 443
+
 # New failures
 LibTest/core/RegExp/Pattern_semantics/firstMatch_CharacterEscape_A06_t02: Fail