RFR: 8296330: Tests: Add layout container snapping tests [v3]

[Andy Goryachev]

On Mon, 7 Nov 2022 19:55:59 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> While checking https://bugs.openjdk.org/browse/JDK-8295078 I found much more layout container which do not snap their children correctly.
>> 
>> The goal of this PR is to add snapping tests for all layout container.
>> After that we can create issues for all broken layout container, fix them and comment in the corresponding line.
>
> Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8296330: Missed two :P

Changes requested by angorya (Author).

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PR: https://git.openjdk.org/jfx/pull/936