RFR: 8316423: [linux] Secondary Stage does not respect Scene's dimensions when shown [v8]

[Thiago Milczarek Sayao]

> The bug on the title happens because `gtk_widget_realize()` was called on the constructor. It creates the internal underlying window  `GdkWindow` and `XWindow` messing the Gtk expected order. It's probably a Mutter change rather than Gtk. But makes sense to not realize it before expected on the gtk/mutter flow.
> 
> I moved the code to get the `GdkWindow` to the realize event.
> 
> Had to change the background function because it's called before realize.
> 
> The initial **Maximized** and **FullScreen** situations are probably a bug on Mutter [filed here](https://gitlab.gnome.org/GNOME/mutter/-/issues/3092).
> 
> I could work-around it on this situation, but it would still happen on later focus request.

Thiago Milczarek Sayao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:

 - Fix unwanted changes
 - Fix unwanted changes
 - Merge branch 'master' into window_size
 - Fix unwanted changes
 - Fix background
 - Revert "Test"
   
   This reverts commit ac7b4da75b9690c42aecd484bb3990866a004074.
 - Test
 - Experiment on not realizing the window
 - Experiment on not realizing the window
 - Re-enable tests
 - ... and 3 more: https://git.openjdk.org/jfx/compare/ba7b899f...315e1b73

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1249/files
  - new: https://git.openjdk.org/jfx/pull/1249/files/891d9407..315e1b73

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1249&range=07
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1249&range=06-07

  Stats: 4662 lines in 104 files changed: 4103 ins; 364 del; 195 mod
  Patch: https://git.openjdk.org/jfx/pull/1249.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1249/head:pull/1249

PR: https://git.openjdk.org/jfx/pull/1249