RFR: 8334739: XYChart.x/yAxisProperty returns incorrect bean

[Markus Mack]

This PR makes the `XYChart` axes properties return the correct parent XYChart object.

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Commit messages:
 - XYChart: Set correct bean of axes properties

Changes: https://git.openjdk.org/jfx/pull/1485/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1485&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334739
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1485.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1485/head:pull/1485

PR: https://git.openjdk.org/jfx/pull/1485