RFR: 8301302: Platform preferences API [v47]

[Michael Strauß]

> Please read [this document](https://gist.github.com/mstr2/9f46f92c98d3c86aa6a0b4224a9a6548) for an introduction to the Platform Preferences API, and how it interacts with the proposed style theme and stage appearance features.

Michael Strauß has updated the pull request incrementally with three additional commits since the last revision:

 - removed unused import
 - javadoc
 - query resource bundles for high-contrast schemes only on Windows

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1014/files
  - new: https://git.openjdk.org/jfx/pull/1014/files/efdab27b..3354782b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1014&range=46
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1014&range=45-46

  Stats: 30 lines in 3 files changed: 9 ins; 10 del; 11 mod
  Patch: https://git.openjdk.org/jfx/pull/1014.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1014/head:pull/1014

PR: https://git.openjdk.org/jfx/pull/1014