RFR: 8260528: Clean glass-gtk sizing and positioning code [v27]

[Thiago Milczarek Sayao]

On Mon, 28 Jun 2021 23:50:31 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

>> This is a new approach to rewrite parts of gtk glass backend to be more clean.
>> 
>> I will provide small "manageable" PR to incrementally make the backend better.
>> 
>> This PR adresses cleanup of the Size and Positioning code. It makes code more "straightforward" and easier to maintain.
>> 
>> Current status (Ubuntu 20.04):
>> ![image](https://user-images.githubusercontent.com/30704286/102702414-1b1b1800-4241-11eb-90bf-8ab737ce2e04.png)
>> 
>> (*) Some of the iconify tests are also failing on the main branch. 
>> 
>> `gradlew -PFULL_TEST=true -PUSE_ROBOT=true :systemTests:test --tests test.robot.javafx.stage.IconifyTest` on a second run produces 4 tests, 2 failures.
>
> Thiago Milczarek Sayao has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix build
>   gtk_widget_set_sensitive has no effect

Closed in favor of #915

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