RFR: 8253597: TreeTableView: must select leaf row on click into indentation region

[Jeanette Winzenburg]

.. but doesn't reliably (see report for details). Fixed in TreeTableCellBehavior to check for visibility of the
disclosureNode.

Added test that failed before and passes after, along with a couple of sanity tests.

Also added an alternative mouseEvent creation path into MouseEventFirer (and test) to work-around
[JDK-8253769](https://bugs.openjdk.java.net/browse/JDK-8253769)

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Commit messages:
 - 8253597: TreeTableView: must select leaf row on click into indentation

Changes: https://git.openjdk.java.net/jfx/pull/313/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=313&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253597
  Stats: 702 lines in 4 files changed: 696 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jfx/pull/313.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/313/head:pull/313

PR: https://git.openjdk.java.net/jfx/pull/313