RFR: 8260528: Clean glass-gtk sizing and positioning code [v25]

[Thiago Milczarek Sayao]

On Fri, 30 Sep 2022 06:49:40 GMT, Johan Vos <jvos at openjdk.org> wrote:

>> Testing:
>> 
>> **master**
>> ![master](https://user-images.githubusercontent.com/30704286/111889893-6e793f80-89c3-11eb-8f38-640e8123794c.png)
>> 
>> **tsayao:glass_gtk_new_position_and_size**
>> ![branch](https://user-images.githubusercontent.com/30704286/111889897-733df380-89c3-11eb-9929-2ed55471638e.png)
>> 
>> `--tests test.robot.javafx.scene.RobotTest` causes some intermittent error but eventually all passes.
>
> @tsayao The work in this PR looks really good. If you want to continue with this, I will review it. There are some conflicts but those can easily be solved.

@johanvos I think I can rework it better now.

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PR: https://git.openjdk.org/jfx/pull/367