RFR: 8313956: focusWithin on parents of a newly-added focused node is not updated [v3]

[Michael Strauß]

> This PR fixes an issue with the way `focusWithin` bits are adjusted in the scene graph. Previously, the `focusWithin` counts of all parents of a removed node would be decreased if the removed node has a non-zero `focusWithin` count. This PR adds logic for the opposite scenario: the `focusWithin` count is increased on all parents of a newly-added node that is already focused (or contains other focused nodes).

Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:

  Correctly handle added node with multiple focuses

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1210/files
  - new: https://git.openjdk.org/jfx/pull/1210/files/fd85c902..a0d230e7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1210&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1210&range=01-02

  Stats: 32 lines in 2 files changed: 31 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1210.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1210/head:pull/1210

PR: https://git.openjdk.org/jfx/pull/1210