RFR: 8090522: Allow support for disabling stage iconification (minimization)

[Paweł Kruszczyński]

`Stage` minimalizing (iconified state) cannot be disabled for the user. The same for `Stage` closable state.
PR adds these features without breaking backward compatibility.

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Commit messages:
 - 8090522: Allow support for disabling stage iconification (minimization)

Changes: https://git.openjdk.java.net/jfx/pull/798/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=798&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8090522
  Stats: 199 lines in 5 files changed: 198 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/798.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/798/head:pull/798

PR: https://git.openjdk.java.net/jfx/pull/798