RFR: JDK-8315569: Tests for the contract of SkinBase.layoutChildren(..) [v3]

[Marius Hanl]

> This PR adds a test that verifies the `SkinBase.layoutChildren(..)` method with different scales.
> While not explicitly documented, this method will receive the snapped and correctly calculated x, y, width and height values, so that children of the Control can be layouted correctly without requiring to do many more calculations regarding padding.

Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8315569: Improve test name and add 2.25 scale

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1229/files
  - new: https://git.openjdk.org/jfx/pull/1229/files/8ae26188..30b14c2e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1229&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1229&range=01-02

  Stats: 256 lines in 2 files changed: 129 ins; 127 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1229.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1229/head:pull/1229

PR: https://git.openjdk.org/jfx/pull/1229