Implement Encoding API

LayoutTests/fast/encoding/api/surrogate-pairs-expected.txt

+Test invalid UTF-16 surrogate pairs with UTF-8 encoding
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+encoded = new TextEncoder('utf-8').encode("abc123")
+decoded = new TextDecoder('utf-8').decode(encoded)
+PASS decoded is "abc123"
+
+encoded = new TextEncoder('utf-8').encode("���")
+decoded = new TextDecoder('utf-8').decode(encoded)
+FAIL decoded should be �. Was ���.
+
+encoded = new TextEncoder('utf-8').encode("���")
+decoded = new TextDecoder('utf-8').decode(encoded)
+FAIL decoded should be �. Was ���.
+
+encoded = new TextEncoder('utf-8').encode("abc���def")
+decoded = new TextDecoder('utf-8').decode(encoded)
+FAIL decoded should be abc�def. Was abc���def.
+
+encoded = new TextEncoder('utf-8').encode("abc���def")
+decoded = new TextDecoder('utf-8').decode(encoded)
+FAIL decoded should be abc�def. Was abc���def.
+
+encoded = new TextEncoder('utf-8').encode("������")
+decoded = new TextDecoder('utf-8').decode(encoded)
+FAIL decoded should be ��. Was ������.
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+