RFR: JDK-8306990: The guarantees given by Region's floor and ceiling functions should work for larger values [v2]

[John Hendrikx]

> Region has floor and ceiling functions that ensure that calling them twice in a row will yield the same result:
> 
>      ceil(x) = ceil(ceil(x))
> 
> However, due to use of a constant `EPSILON` which is added/subtracted before doing the rounding, this only works for small numbers (in the range of 0-50 approximately).  For larger values and scales, rounding errors can easily occur.  This is visible as artifacts on screen where controls are a pixel wider than they should be.
> 
> The use of the `EPSILON` constant is incorrect, as its value depends on the magnitude of the value in question (as magnitude increases, the fractional precision decreases).
> 
> The Math class offers the function `ulp` that should be used here.  It represents the smallest possible change in value for a given double.
> 
> Extending the existing test case `snappingASnappedValueGivesTheSameValueTest` to use larger magnitude numbers exposes the problems.

John Hendrikx 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 three additional commits since the last revision:

 - Print seed if test fails
 - Merge branch 'master' into feature/ceil-fix
 - Fix Region ceil/floor function guarantees to be more accurate

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1118/files
  - new: https://git.openjdk.org/jfx/pull/1118/files/ee87060c..65e1475a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1118&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1118&range=00-01

  Stats: 731 lines in 31 files changed: 186 ins; 469 del; 76 mod
  Patch: https://git.openjdk.org/jfx/pull/1118.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1118/head:pull/1118

PR: https://git.openjdk.org/jfx/pull/1118