By default return an 'UTF8Unmarked' object.  Removed unused 'utf8EncodingWithMarkers' attribute.
Added counter mode in InternalGetBytes.
Added methods InternalGetBytesCount and InternalGetBytesEncode for improving readability.
Reverted all changes in 'System.Text/Encoding.cs' and disabled the emitIdentifier feature in the new 'System.Text/UTF8Encoding.cs'.
bugfix: accept zero-length input buffer in 'InternalGetChars' for building void strings.