[jdk11u-dev] RFR: 8292182: [TESTLIB] Enhance JAXPPolicyManager to setup required permissions for jtreg version 7 jar

[Aleksey Shipilev]

Clean backport to enable jtreg 7 for jaxp tests.

Additional testing:
 - [x] `jaxp:all` still passes with jtreg-6.2
 - [x] `jaxp:all` now fully passes with jtreg-7.3.1

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Commit messages:
 - Backport aa5b71893307b9fe6137bc3541edccaab73735ac

Changes: https://git.openjdk.org/jdk11u-dev/pull/2558/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2558&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292182
  Stats: 8 lines in 1 file changed: 3 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2558.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2558/head:pull/2558

PR: https://git.openjdk.org/jdk11u-dev/pull/2558