RFR: 8252238: TableView: Editable (pseudo-editable) cells should respect the row editability [v2]

[Marius Hanl]

> This PR enables Tree- and TableCells to also check the row editability when an edit should happen. With this a Tree- or TableCell is not editable, when the row where the cell is in is not.
> 
> While this PR fixes the problem described in the ticket, it does not fix the example.
> This is due the example uses the **CheckBoxTableCell**, which is a ready-to-use subclass of **TableCell**. 
> 
> While looking into this, I found out that multiple sub implementations still have this issue, but the fix is not always the same, e.g. CheckBoxTableCell should disable the CheckBox (in **updateItem**), while the ChoiceBoxTableCell should check the row editability in the **startEdit** method (like this PR does).
> 
> I created a follow-up issues for fixing all the sub Tree- and TableCell implementation which do not count the row editability in:
> [JDK-8268295](https://bugs.openjdk.java.net/browse/JDK-8268295)

Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:

  Addressed review comments

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/529/files
  - new: https://git.openjdk.java.net/jfx/pull/529/files/e40be321..e35bf49a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=529&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=529&range=00-01

  Stats: 122 lines in 3 files changed: 116 ins; 1 del; 5 mod
  Patch: https://git.openjdk.java.net/jfx/pull/529.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/529/head:pull/529

PR: https://git.openjdk.java.net/jfx/pull/529