RFR: 8303530: Redefine JAXP Configuration File [v13]

[Joe Wang]

> Add a system property, jdk.xml.config.file, to return the path to a custom JAXP configuration file. The current configuration file, jaxp.properties, that the JDK supports will become the default configuration file.
> 
> CSR: https://bugs.openjdk.org/browse/JDK-8303531
> 
> Tests: XML SQE and JCK tests passed.

Joe Wang has updated the pull request incrementally with one additional commit since the last revision:

  Changes after many iterations in 3 weeks: added intro, streamlined sections leading to the Configuration File section with most of the text edited; removed duplicate sections in implNote; Other adjustments reflecting these changes.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/12985/files
  - new: https://git.openjdk.org/jdk/pull/12985/files/6506451c..98d9417b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12985&range=12
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12985&range=11-12

  Stats: 624 lines in 6 files changed: 272 ins; 256 del; 96 mod
  Patch: https://git.openjdk.org/jdk/pull/12985.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12985/head:pull/12985

PR: https://git.openjdk.org/jdk/pull/12985