Implement Encoding API

LayoutTests/fast/encoding/api/end-of-file-expected.txt

+Edge cases around non-fatal errors at EOF
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS new TextDecoder('utf-8', {fatal: true}).decode(new Uint8Array([0xff])) threw exception EncodingError: The encoded data was not valid..
+
+Should not throw or hang:
+new TextDecoder('utf-8').decode(new Uint8Array([0xff]))
+
+FAIL new TextDecoder('utf-16', {fatal: true}).decode(new Uint8Array([0x00])) should throw an exception. Was .
+
+Should not throw or hang:
+new TextDecoder('utf-16').decode(new Uint8Array([0x00]))
+
+FAIL new TextDecoder('utf-16be', {fatal: true}).decode(new Uint8Array([0x00])) should throw an exception. Was .
+
+Should not throw or hang:
+new TextDecoder('utf-16be').decode(new Uint8Array([0x00]));
+PASS successfullyParsed is true
+
+TEST COMPLETE
+