Implement TrimStart TrimEnd and aliases (#4102)

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

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

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

@@ -0,0 +1,29 @@
+// 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 = "  asd  ";
+assert(test.trimStart() === "asd  ")
+assert(test.trimStart().length === 5)
+assert(test.trimLeft() === "asd  ")
+assert(test.trimLeft().length === 5)
+assert(String.prototype.trimStart === String.prototype.trimLeft)
+
+assert(test.trimEnd() === "  asd")
+assert(test.trimEnd().length === 5)
+assert(test.trimRight() === "  asd")
+assert(test.trimRight().length === 5)
+assert(String.prototype.trimEnd === String.prototype.trimRight)
+
+assert(test.trim() === "asd")
+assert(test.trim().length === 3)