RFR: 8251481: TableCell accessing row: NPE on auto-sizing [v2]

[Marius Hanl]

> This PR will fix a simple NPE which may happens when using the `TableRow` inside a `TableCell` during the initial auto sizing.
> In the auto sizing code, no `TableRow` is set, therefore `getTableRow()` will return null and it is not possible to e.g. access the row item.
> 
> This is fixed by adding the `TableRow` in the `resizeColumnToFitContent` method, similar as it is already done for the `TreeTableView` (`TreeTableRow`).

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

  8251481: Added TreeTableCellTest / reordered TableCellTest and added more details to it (javadoc)

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/716/files
  - new: https://git.openjdk.java.net/jfx/pull/716/files/0ba6b283..30dd77e9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=716&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=716&range=00-01

  Stats: 65 lines in 2 files changed: 45 ins; 19 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/716.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/716/head:pull/716

PR: https://git.openjdk.java.net/jfx/pull/716