RFR: JDK-8298060: Fix precision bug in gesture recognizer classes [v2]

[John Hendrikx]

> This includes a fix for the precision problem we've found as part of the graphics warnings clean ups.
> 
> I've included two commits, one with just the minimal fix, and one with the clean ups. I can drop off the 2nd commit if it is deemed to be of no added value.

John Hendrikx has updated the pull request incrementally with two additional commits since the last revision:

 - Make RotateGestureRecognizer easier to test
 - Revert all changes to RotateGestureRecognizer

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Changes:
  - all: https://git.openjdk.org/jfx/pull/966/files
  - new: https://git.openjdk.org/jfx/pull/966/files/eef709a2..ce9979fc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=966&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=966&range=00-01

  Stats: 484 lines in 4 files changed: 372 ins; 24 del; 88 mod
  Patch: https://git.openjdk.org/jfx/pull/966.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/966/head:pull/966

PR: https://git.openjdk.org/jfx/pull/966