RFR: 8271474: Tree-/TableCell: inconsistent edit event firing pattern

[Jeanette Winzenburg]

this PR fixes the inconsistent event firing pattern in cell's xxEdit methods (please see the issue for more details):

- fires event if column != null
- accesses table state if table != null

The first requires a change in CellEditEvent which now allows null table in its constructor.

Added tests that failed/passed before/after the fix (along with some that also passed before for complete coverage of state permutations). Changed two old test methods which passed/failed before/after the fix - but did test the wrong thingy anyway ;)

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Commit messages:
 - 8271474: Tree-/TableCell: inconsistent edit event firing pattern

Changes: https://git.openjdk.java.net/jfx/pull/620/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=620&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271474
  Stats: 404 lines in 12 files changed: 358 ins; 22 del; 24 mod
  Patch: https://git.openjdk.java.net/jfx/pull/620.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/620/head:pull/620

PR: https://git.openjdk.java.net/jfx/pull/620