RFR: 8354943: [Linux] Simplify and update glass gtk backend: window sizing, positioning, and state management issues [v15]

[Thiago Milczarek Sayao]

> This is a continuation to [JDK-8236651](https://bugs.openjdk.org/browse/JDK-8236651) and it aims to stabilize the linux glass gtk backend.
> 
> 
> Overall, it has been made more robust within its scope, particularly in terms of sizing, positioning, and state management.
> 
> List of changes:
> 1. Use GDK for creating Windows. Since we paint directly to the underlying XWindow, creating a GtkWidget for the window is unnecessary and results in unused GTK resources. Additionally, avoiding the use of a GtkWidget eliminates the need for workarounds caused by conflicting GTK behavior—such as setting the initial window state, position, or size.
> 2. It aligns with X11's asynchronous behavior by reporting geometry changes only upon receiving a configure event, since requests to the window manager aren't guaranteed to be honored. However, changes are still reported immediately in special cases, such as before the window is realized. For example, a request to move the window to (0, 0) might be overridden by the window manager, placing it in the top-right corner instead.
> 3. States (fullscreen, maximized and iconify) are now reported back to Java when it actually happens rather than immediately (except when not realized);
> 4. When a window is maximized, it will ignore geometry changes and restore to the geometry it had prior to being maximized. After some testing, I believe this is the best behavior for platform compatibility;
> 5. Unifies the WindowContext class: previously, there were three separate classes—two of which (for applets and Java Web Start) were removed, leaving only one. However, the supporting infrastructure was still there partially. [Unify WindowContext in glass-gtk](https://bugs.openjdk.org/browse/JDK-8305768)
> 6. Tests were added and re-enabled to ensure everything works correctly. The stage tests now cover various StageStyle configurations, as I found that `DECORATED` stages often behave differently from `UNDECORATED` or `UTILITY` stages;
> 7. Added Logs for debugging. Enable it with ` -PCONF=DebugNative`;
> 8. Old work-arounds dating back to Ubuntu 16.04 with Compiz were removed. 
> 
> A simple manual test is provided:
> `java @build/run.args tests/manual/stage/TestStage.java `
> 
> 
> List of fixed issues:
> 
> 1. [[Linux] Stage.setMaximized() before show() does not persist](https://bugs.openjdk.org/browse/JDK-8316425)
> 3. [[Linux] Intermittent test failure in IconifyTest.canIconifyDecoratedStage](https://bugs.openjdk.org/browse/JDK-8316891)
> 4. [[Linux] Initial window position is not ...

Thiago Milczarek Sayao has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 16 commits:

 - Merge master
 - Merge branch 'master' into 8354943
   
   # Conflicts:
   #	tests/system/src/test/java/test/javafx/scene/RestoreSceneSizeTest.java
 - TestStage
 - - Improve TestStage
   - Notify maximize/fullscreen before show on native side
 - Fix test on SizingTest
 - Remove state precedence tests
 - Use GDK for windowing
 - Remove old comment
 - - Remove unused var
 - - Re-enable DualWindowTest
 - ... and 6 more: https://git.openjdk.org/jfx/compare/498b7e4c...2bc86379

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Changes: https://git.openjdk.org/jfx/pull/1789/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1789&range=14
  Stats: 3970 lines in 28 files changed: 2717 ins; 758 del; 495 mod
  Patch: https://git.openjdk.org/jfx/pull/1789.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1789/head:pull/1789

PR: https://git.openjdk.org/jfx/pull/1789