Rework RegExp engine and add support for proper unicode matching (#3746)

This change includes several bugfixes, general improvements, and support
for additional features.
- Added full support for web compatibility syntax defined in Annex B
- Implemented parsing and matching patterns in unicode mode
- Fixed capture results when iterating with nested capturing groups
- Significantly reduced regexp bytecode size
- Reduced stack usage during regexp execution
- Improved matching performance

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

jerry-core/ecma/builtin-objects/ecma-builtin-json.c

@@ -174,18 +174,13 @@ ecma_builtin_json_parse_string (ecma_json_token_t *token_p) /**< token argument
         }
         case LIT_CHAR_LOWERCASE_U:
         {
-          if ((end_p - current_p <= ECMA_JSON_HEX_ESCAPE_SEQUENCE_LENGTH))
+          uint32_t hex_value = lit_char_hex_lookup (current_p + 1, end_p, ECMA_JSON_HEX_ESCAPE_SEQUENCE_LENGTH);
+          if (hex_value == UINT32_MAX)
           {
             goto invalid_string;
           }
 
-          ecma_char_t code_unit;
-          if (!(lit_read_code_unit_from_hex (current_p + 1, ECMA_JSON_HEX_ESCAPE_SEQUENCE_LENGTH, &code_unit)))
-          {
-            goto invalid_string;
-          }
-
-          ecma_stringbuilder_append_char (&result_builder, code_unit);
+          ecma_stringbuilder_append_char (&result_builder, (ecma_char_t) hex_value);
           current_p += ECMA_JSON_HEX_ESCAPE_SEQUENCE_LENGTH + 1;
           break;
         }