Implement \u{hex} support. (#3447)

A large rework because surrogate pairs must be combined.

Currently only the 0x10C80..0x10CF2 is accepted as valid identifier character from the non-basic plane.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

tests/jerry/es2015/identifier-escape.js

@@ -0,0 +1,36 @@
+/* Copyright JS Foundation and other contributors, http://js.foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+function check_syntax_error (code) {
+  try {
+    eval(code)
+    assert (false)
+  } catch (e) {
+    assert (e instanceof SyntaxError)
+  }
+}
+
+eval("\u{000010C80}: break \ud803\udc80")
+eval("\\u{10C80}: break \ud803\udc80")
+eval("$\u{000010C80}$: break $\ud803\udc80$")
+eval("$\\u{10C82}$: break $\ud803\udc82$")
+
+assert("\u{000010C80}".length === 2)
+assert("x\u{010C80}y".length === 4)
+assert("\u{10C80}" === "\ud803\u{dc80}")
+assert("\u{0}\x01" === "\u0000\u0001")
+
+/* Surrogate pairs are not combined if they passed as \u sequences. */
+check_syntax_error("\\u{10C80}: break \\ud803\\udc80");