RFR: 8299968: Second call to Stage.setScene() create sizing issue with uiScale > 1.0

[Lukasz Kostyra]

Issue happened during setting a new Scene - updating a new View was done while the Window reference it kept was null. This caused it to default scaling values to 1.0f (or 100%) while processing a resize notification, which for high DPI screens with scaling different than 100% caused UI issues.

Resolved by splitting `_setView()` native call into two parts - first one sets the view, then back in JVM side we set a correct Window reference, then we trigger the notification. It has to be triggered from native side, because Windows backend of Glass sends back new width/height pulled from WinAPI `::GetClientRect()` call.

In process of working on this issue I also found another scenario causing the same problem - calling `Stage.setScene()` after `Stage.show()`. The patch fixed that case as well.

Added a system test which is supposed to check for above issues. I didn't limit it to run only on platforms with UI scaling enabled because it also serves as a good sanity check in case there are some other changes to code that might move/scale the UI unwantingly. I tested this patch both on macOS Ventura and Windows 11, with `d9c091f` all tests pass while without `d9c091f` on Windows tests `testShowAndSetScene` and `testSecondSetScene` fail as expected.

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Commit messages:
 - SetSceneScalingTest: Properly time test elements
 - Add test for various setScene-show interactions
 - Fetch View's size after it has a valid Window ptr

Changes: https://git.openjdk.org/jfx/pull/1054/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1054&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299968
  Stats: 250 lines in 8 files changed: 247 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1054.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1054/head:pull/1054

PR: https://git.openjdk.org/jfx/pull/1054