RFR: 8296330: Tests: Add layout container snapping tests

[Marius Hanl]

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.

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Commit messages:
 - 8296330: Tests: Add layout container snapping tests

Changes: https://git.openjdk.org/jfx/pull/936/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=936&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296330
  Stats: 165 lines in 1 file changed: 165 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/936.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/936/head:pull/936

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