[jfx11u] RFR: 8273998: Clarify specification for Window properties controlled by the window manager

[Kevin Rushforth]

Clean backport to `jfx11u`.

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

Commit messages:
 - 8273998: Clarify specification for Window properties controlled by the window manager

Changes: https://git.openjdk.java.net/jfx11u/pull/99/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=99&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273998
  Stats: 84 lines in 2 files changed: 59 ins; 4 del; 21 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/99.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/99/head:pull/99

PR: https://git.openjdk.java.net/jfx11u/pull/99