RFR: 8348100: Tooltips cannot be instantiated on background thread [v3]

[Andy Goryachev]

> ## Root Cause
> navigating up the parent hierarchy during CSS processing in a background thread encounters a null parent, causing the NPE.  The null parent comes from a static Toolkit.BEHAVIOR field.
> 
> ## Solution
> avoid that code path if not in the fx application thread.

Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:

  behavior

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1696/files
  - new: https://git.openjdk.org/jfx/pull/1696/files/3ba9c9a2..6f48657a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1696&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1696&range=01-02

  Stats: 55 lines in 2 files changed: 24 ins; 24 del; 7 mod
  Patch: https://git.openjdk.org/jfx/pull/1696.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1696/head:pull/1696

PR: https://git.openjdk.org/jfx/pull/1696