RFR (JDK 13/java.xml) 8222415: Xerces 2.12.0: Parsing Configuration

[Joe Wang]

Please review an update from Xerces in the configuration area. The patch 
contains changes not easily measurable with test (e.g. a few bytes for a 
parse, or small leaks for a file as large as a GB, or none at all). But 
the change does improve in that a method ( readAndBuffer) that 
explicitly buffers was provided so that the processes that required 
buffer all call it instead of the general read method. While there's a 
small test added, the testing  was focused on getting the existing ones 
to pass.

All XML-related tests in the core tests and JCK passed.
JBS: https://bugs.openjdk.java.net/browse/JDK-8222415
webrevs: http://cr.openjdk.java.net/~joehw/jdk13/8222415/webrev/

Thanks,
Joe