Implement String.fromCodePoint method (#3281)

The algorithm is based on ECMA-262 v6, 21.1.2.2

JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

tests/jerry/es2015/string-fromcodepoint.js

@@ -0,0 +1,64 @@
+// 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.
+
+// Tests with valid inputs
+assert(String.fromCodePoint(42) === "*")
+assert(String.fromCodePoint(65, 90) === "AZ");
+assert(String.fromCodePoint(0x404) === "Є");
+assert(String.fromCodePoint(194564) === "你");
+assert(String.fromCodePoint(0x1D306, 0x61, 0x1D307) === "𝌆a𝌇");
+assert(String.fromCodePoint(0x1F303) === "🌃");
+
+// Tests with invalid inputs
+try {
+    assert(String.fromCodePoint('_'));
+    assert(false);
+} catch (e) {
+    assert(e instanceof RangeError);
+}
+
+try {
+    assert(String.fromCodePoint(Infinity));
+    assert(false);
+} catch (e) {
+    assert(e instanceof RangeError);
+}
+
+try {
+    assert(String.fromCodePoint(-1));
+    assert(false);
+} catch (e) {
+    assert(e instanceof RangeError);
+}
+
+try {
+    assert(String.fromCodePoint(3.14));
+    assert(false);
+} catch (e) {
+    assert(e instanceof RangeError);
+}
+
+try {
+    assert(String.fromCodePoint(3e-2));
+    assert(false);
+} catch (e) {
+    assert(e instanceof RangeError);
+}
+
+try {
+    assert(String.fromCodePoint(NaN));
+    assert(false);
+} catch (e) {
+    assert(e instanceof RangeError);
+}