RFR: 8355615: ConcurrentModificationException creating MenuBar on background thread [v2]

[Andy Goryachev]

> Moving MenuBarSkin initialization code to install() which always happens in the FX Application Thread.
> 
> Also, ensure that the reverse process also happens in the FX application thread.

Andy Goryachev 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:

 - Merge remote-tracking branch 'origin/master' into 8355615.menubar
 - in fx thread
 - install

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1795/files
  - new: https://git.openjdk.org/jfx/pull/1795/files/d5bea119..a1552f63

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1795&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1795&range=00-01

  Stats: 84 lines in 8 files changed: 41 ins; 15 del; 28 mod
  Patch: https://git.openjdk.org/jfx/pull/1795.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1795/head:pull/1795

PR: https://git.openjdk.org/jfx/pull/1795