RFR: 8333919: dragViewOffsetX/dragViewOffsetY are ignored for the dragView image [v4]

[Lukasz Kostyra]

> When fixing [JDK-8233955](https://bugs.openjdk.org/browse/JDK-8233955) offset calculation was left out, which made Dragboard offset API not work on macOS.
> 
> This change fixes this mistake. Now drag image should be properly offset.

Lukasz Kostyra has updated the pull request incrementally with one additional commit since the last revision:

  Merge two if image != nil statements together
  
  Those were unnecessarily split

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1532/files
  - new: https://git.openjdk.org/jfx/pull/1532/files/41cd6755..f6d065ce

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1532&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1532&range=02-03

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1532.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1532/head:pull/1532

PR: https://git.openjdk.org/jfx/pull/1532