RFR: JDK-8187314: All Cells: must show backing data always

[Marius Hanl]

Before, the `updateItem` method was called with the new value that was committed via `commitEdit()`.
This is problematic as developers may setup a commit handler via `setOnEditCommit`, which may reject the edit (or change the value otherwise).
We therefore do call the `updateItem(-1)` which will also call `updateItem` but with the real underlying value.

Changed and added tests for all 4 cells.

-------------

Commit messages:
 - JDK-8187314: All Cells: must show backing data always

Changes: https://git.openjdk.org/jfx/pull/1197/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1197&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8187314
  Stats: 110 lines in 8 files changed: 94 ins; 2 del; 14 mod
  Patch: https://git.openjdk.org/jfx/pull/1197.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1197/head:pull/1197

PR: https://git.openjdk.org/jfx/pull/1197