RFR: 8354943: [Linux] Simplify and update glass gtk backend: window sizing, positioning, and state management issues [v10]

[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. It embraces the asynchronous nature of X11 by reporting geometry changes only upon receiving a configure event, rather than immediately as before. This is because it merely requests changes from the window manager, which may or may not honor them. However, it still reports changes immediately in certain special cases, such as when the window has not yet been realized (i.e., when the window has not actually been created yet). One scenario where this behavior is evident is when we request the window to move to position (0, 0), but the window manager instead places it in the top-right corner where panels converge.
> 2. FullScreen now keeps track of geometry changes and apply them on restore as documented on Stage.java. No geometry changes affects the FullScreen state;
> 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 also provided but I would prefer to move it's functionality to monkey tester:
> `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)
> 2. [[Linux] Intermittent test failure in IconifyTest.canIconifyDecoratedStage](https://bugs.openjdk.o...

Thiago Milczarek Sayao has updated the pull request incrementally with one additional commit since the last revision:

  Use GDK for windowing

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1789/files
  - new: https://git.openjdk.org/jfx/pull/1789/files/61230d59..61b7593d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1789&range=09
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1789&range=08-09

  Stats: 1899 lines in 13 files changed: 1093 ins; 531 del; 275 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