RFR: 8244075: Accelerator of ContextMenu's MenuItem is not removed when ContextMenu is removed from Scene [v2]

[Ambarish Rapte]

> Issue:
> There are several issues related to Accelerator of MenuItem of a ConextMenu set on Control.
> 1. Accelerator of ContextMenu's MenuItem is not removed when ContextMenu is removed from Scene
> 2. Accelerator is not updated correctly when the Control is removed from a Scene and Added to a different Scene
> 3. Accelerator is not removed from Scene when the anchor node is removed from Scene and then it's ContextMenu is set to null
> 
> Fix:
> The accelerator should be added or removed correctly according to the Scene property of the anchor node. 
> The issue#3 in above list is only fixed for Button and fails for other Controls. A test is added for this scenario and I shall report a new issue to address it.
> Added tests that fails before and pass after the fix.

Ambarish Rapte has updated the pull request incrementally with one additional commit since the last revision:

  update @ignore() with bugid

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/515/files
  - new: https://git.openjdk.java.net/jfx/pull/515/files/f50a0232..45a4db9b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=515&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=515&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/515.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/515/head:pull/515

PR: https://git.openjdk.java.net/jfx/pull/515