RFR: 8255415: Nested calls to snap methods in Region give different results [v3]

[Jose Pereda]

> As discussed in the [JBS issue](https://bugs.openjdk.java.net/browse/JDK-8199592), when snapping an already snapped value (either intentionally or by  mistake), the result should be the same, otherwise we'll be jumping unnecessary from a valid pixel to another pixel.
> 
> This PR provides a fix to `snapSizeXX` methods used in `Region`, which ultimately use `Math.ceil`, by subtracting an epsilon value to scaled value before ceiling, to ensure snapping a snapped value gives the same value.
> 
> A test to verify `snapSizeX` and `snapSizeY` with 1000 random values, and 6 different UI scales is provided.
> For the 1.0, 1.25, 1.5 and 2.0 UI scales, the current approach works fine. Only for 1.75 and the random 1.374562997 value fails (the test fails for around 2% of the values with 1.75 and around 10% with 1.374562997).
> With the proposed fix, it doesn't fail at all.

Jose Pereda has updated the pull request incrementally with one additional commit since the last revision:

  Add javadoc to scaledCeil

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/336/files
  - new: https://git.openjdk.java.net/jfx/pull/336/files/5ff5fcce..988afefb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=336&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=336&range=01-02

  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/336.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/336/head:pull/336

PR: https://git.openjdk.java.net/jfx/pull/336