6229811: Several codepoints in EUC_TW failed in roundtrip conversion
Re-write EUC_TW charset to address the size and roundtrip issue.
Reviewed-by: alanb
6636319: Encoders should implement isLegalReplacement(byte[] repl)
Optimized new String(byte[], cs/csn) and String.getBytes(cs/csn) for speed and memory consumption in singlebyte case.
Reviewed-by: alanb