RFR: 8260528: Clean glass-gtk sizing and positioning code [v35]

[Kevin Rushforth]

On Sun, 18 Dec 2022 20:06:57 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

> **About Ubuntu 16.04:**
> 
> * `RestoreSceneSizeTest` should be fixed;

Confirmed. This now passes for me.

> * I kept `gtk_window_focus_on_map` `TRUE` on Compiz - so it will behave as before;
> * I introduced a `WindowManager` enum in case different work arounds are needed for other window managers;

OK, I'll test it towards the middle of this week (I don't have direct access to my 16.04 system at the moment).

> * About Live resizing: master branch does not live resize as well (at least on my VM);

OK. This is not worth worrying about in any case.

> **About the black area**
> 
> * It does not happen on a Ubuntu 20.04 VM I installed, but I did some overall improvements on consistency while testing on 16.04. Maybe it's gone.

I still see the black band consistently on my Ubuntu 20.04 VM.

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PR: https://git.openjdk.org/jfx/pull/915