Implement String.padStart and String.padEnd (#3999)

Based on: https://tc39.es/ecma262/#sec-string.prototype.padstart

JerryScript-DCO-1.0-Signed-off-by: Bela Toth tbela@inf.u-szeged.hu

tests/jerry/es.next/string-prototype-padding.js

@@ -0,0 +1,81 @@
+/* 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.
+ */
+
+var test = "bar"
+
+assert(test.padStart("5", "foo") === "fobar")
+assert(test.padStart(6, "foo") === "foobar")
+assert(test.padEnd(5, "baz") === "barba")
+assert(test.padEnd(6, "baz") === "barbaz")
+
+// Check for negative value
+assert(test.padStart(-5, "foo") === "bar")
+assert(test.padEnd(-5, "foo") === "bar")
+
+// 21.1.3.15.1.6
+assert(test.padStart(10) === "       bar")
+assert(test.padEnd(10) === "bar       ")
+
+// Empty FilString
+assert(test.padEnd(10, "") === "bar")
+assert(test.padStart(10, "") === "bar")
+
+// Check with unicode surrogate characters
+// 𐋀 = [55296, 57024]
+var unicode_padded = "a".padStart(4 ,"𐋀")
+assert(unicode_padded.charCodeAt(0) == 55296)
+assert(unicode_padded.charCodeAt(1) == 57024)
+assert(unicode_padded.charCodeAt(2) == 55296)
+assert(unicode_padded.charCodeAt(3) == 97)
+
+unicode_padded = "a".padEnd(4 ,"𐋀")
+assert(unicode_padded.charCodeAt(0) == 97)
+assert(unicode_padded.charCodeAt(1) == 55296)
+assert(unicode_padded.charCodeAt(2) == 57024)
+assert(unicode_padded.charCodeAt(3) == 55296)
+
+// 𐋂 = [55296, 57026]
+unicode_padded = "𐋂".padStart(4 ,"𐋀")
+assert(unicode_padded.charCodeAt(0) == 55296)
+assert(unicode_padded.charCodeAt(1) == 57024)
+assert(unicode_padded.charCodeAt(2) == 55296)
+assert(unicode_padded.charCodeAt(3) == 57026)
+
+// Check for errors in length
+try {
+  test.padStart(Symbol("Will this fail?"), "It should" )
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+try {
+  test.padEnd(Symbol("Will this fail?"), "It should" )
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+// Check for errors in fillString
+try {
+  test.padStart(10, Symbol("Fail, this should. " ))
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+try {
+  test.padEnd(10, Symbol("Fail, this should. " ))
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}