RFR: 8277000: Tree-/TableRowSkin: replace listener to fixedCellSize by live lookup [v4]

[Marius Hanl]

> This PR improves the `Tree-/TableRowSkin` code by doing a normal live lookup for the `fixedCellSize` instead of adding listener just to update variables(`fixedCellSizeEnabled` and `fixedCellSize`) which can otherwise be also just lookup'd without the hassle of listeners.
> 
> While this is mostly a cleanup, it does improve the state of the `Tree-/TableRow`, as when the `TableRowSkinBase` constructor is called, the variables are not yet set.
> 
> It is also consistent with the other cells, see also [JDK-8246745](https://bugs.openjdk.org/browse/JDK-8246745).
> Helps a bit with [JDK-8185887](https://bugs.openjdk.org/browse/JDK-8185887) (https://github.com/openjdk/jfx/pull/1644), but as written above, not required as there is no (visible) effect.

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

  Use virtualFlow directly

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1645/files
  - new: https://git.openjdk.org/jfx/pull/1645/files/e6595b8f..9b12fbf7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1645&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1645&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1645.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1645/head:pull/1645

PR: https://git.openjdk.org/jfx/pull/1645