parse method takes CharSequence, not String

Submitted by David Bau, entered initially by Joe Fialli

For javax.xml.datatype.Duration and javax.xml.datatype.XMLGregorianCalendar,
the parser methods have a parameter of type String. To enable efficient
implementations that take advantage of java.nio, it would be preferable
if these parse methods took a CharSequence instead. In JDK 1.4, String
implements CharSequence.

Note that javax.xml.bind.DatatypeConverterInterface and DatatypeConverter
would also need to be changed to make the most of efficiencies being requested
by this change.
#### Environment
Operating System: All
Platform: All
#### Affected Versions
[2.0 draft]

Start by locating the declarations for javax.xml.datatype.Duration, XMLGregorianCalendar, DatatypeConverterInterface, and DatatypeConverter. Review the existing String-based parse methods and the compatibility implications of changing them to CharSequence; the work is done when the affected API changes and their required compatibility coverage are agreed and implemented.

Written by the indexing model from the issue text.