RFR: 8349091: Charts: exception initializing in a background thread [v9]

[Andy Goryachev]

> Root Cause:
> (Multiple) properties are getting bound to the global `Platform.accessibilityActive` property. Binding (and I say, accessing) of properties is not thread-safe.
> 
> I also changed the design a bit.  Originally, every symbol in a chart had its `focusTraversableProperty` bound to `Platform.accessibilityActive` in order to enable the accessibility navigation across the chart data points.  This is rather inefficient, as the property has to manage (thousands?) of listeners.
> 
> Instead, a single boolean property is added to each chart, with a listener added to it which iterates over data symbols to toggle the `focusTraversableProperty` directly.
> 
> The exact moment when the new property gets bound is also important, and has to happen in the FX application thread.
> 
> With this change, it is safe to create and populate charts with data in a background thread.
> 
> ---
> 
> ## NOTES
> 
> 1. It looks like the `Platform.accessibilityActive` property never transitions back to false  after it transitioned to true.  Some say it is because there is no mechanism in the platform to get notified which cannot possibly be true.
> 2. The javadoc for `Platform.accessibilityActiveProperty()` method stipulates that "_This method may be called from any thread_" which is patently not true as the current implementation is simply not thread-safe.
> 
> ## Note to the Reviewers
> 
> To avoid merge conflicts, the preferred order of integrations:
> 
> #1697 
> #1713 
> #1717

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

  review comments

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1697/files
  - new: https://git.openjdk.org/jfx/pull/1697/files/fc40e9d6..509c0519

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1697&range=08
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1697&range=07-08

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1697.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1697/head:pull/1697

PR: https://git.openjdk.org/jfx/pull/1697