RFR: 8296330: Tests: Add layout container snapping tests [v4]

[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.

Marius Hanl has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' of https://github.com/openjdk/jfx into 8296330-snapping-tests
 - 8296330: Renamed DELTA to EPSILON
 - 8296330: Missed two :P
 - 8296330: Added javadoc, made delta a constant, reordered working container on top and renamed ContainerInstruction to ContainerCreator
 - 8296330: Tests: Add layout container snapping tests

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/936/files
  - new: https://git.openjdk.org/jfx/pull/936/files/2d5e5801..fa8bc1ba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=936&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=936&range=02-03

  Stats: 436 lines in 112 files changed: 239 ins; 13 del; 184 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