Fix TypedArray.slice with external array buffer (#3080)

In case of TypedArrays which were constructed with an ArrayBuffer
the `slice` method incorrectly added the `byteOffset` value of
when the elements were copied.

There is no need to add the `byteOffset` value for the ArrayBuffer's
contents pointer as it is already added by the `ecma_typedarray_get_buffer`
call.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.u-szeged@partner.samsung.com

tests/jerry/es2015/regression-test-issue-3078.js

@@ -0,0 +1,21 @@
+// 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 arrb = new ArrayBuffer(13);
+var arr = new Uint8Array(arrb, 9);
+for (var idx = 0; idx < arr.length; idx++) {
+  arr[idx] = idx + 1;
+}
+
+assert(arr.slice(1).toString() == "2,3,4");