Add support of escaping backslash and backtick to String.raw (#3736)

Template literals already supports escaping backslash and backtick,
this commit enables escaping this in String.raw.
It also fixes invalid behaviour of String.raw when using
new line character.

JerryScript-DCO-1.0-Signed-off-by: Rafal Walczyna r.walczyna@samsung.com

tests/jerry/es2015/string-raw-crash-escaping-backslash.js

@@ -0,0 +1,26 @@
+/* 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.
+ */
+
+/* This test must be left unchanged - testing JerryScript crash */
+
+try
+{
+  var s = 'print(String.raw`\\`)\n// `';
+  eval (s)
+  asserts(false)
+}
+catch (error)
+{
+}

tests/jerry/es2015/string-raw.js

@@ -62,3 +62,10 @@ var raw = new Proxy({length: 2, 0: '', 1: ''}, { get: function(o, k) { get.push(
 var p = new Proxy({raw: raw}, { get: function(o, k) { get.push(k); return o[k]; }});
 String.raw(p);
 assert(get + '' === "raw,length,0,1");
+
+assert(String.raw`\\` == "\\\\")
+assert(String.raw`\`` == "\\`")
+assert(String.raw`\
+\
+` == "\\\n\\\n")
+assert(String.raw`\
` == "\\\u2029")