AbstractLoggingInterceptor tests and improvements

Improvements for AbstractLoggingInterceptor:

1. fall back to logging raw XML payload if pretty-printing fails
2. ensure capacity in the output based on the raw XML string size
3. write directly (and improve performance) to the output StringBuilder using custom Writer
4. read directly (and improve performance) from the StringWriter buffer using custom Reader
5. contruct XMLStreamReader directly rather than going via Source
6. do not call XMLStreamWriter.close() before getting contents for truncated or invalid XML because some writers misbehave (are extra helpful) in a way unfit for logging.
7. additional javadoc / comments
8. additional test cases