RFR: 8285197: TableColumnHeader: calc of cell width must respect row styling (TreeTableView) [v2]

[Robert Lichtenberger]

> Separate test class added for TreeTableView case.
> Fix is analogous to JDK-8251480.

Robert Lichtenberger has updated the pull request incrementally with two additional commits since the last revision:

 - 8285197: TableColumnHeader: calc of cell width must respect row styling (TreeTableView)
   
   Test class cosmetic cleanups #2.
 - 8285197: TableColumnHeader: calc of cell width must respect row styling (TreeTableView)
   
   Test class cosmetic cleanups.

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/779/files
  - new: https://git.openjdk.java.net/jfx/pull/779/files/38d930a8..68f7c806

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=779&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=779&range=00-01

  Stats: 13 lines in 1 file changed: 3 ins; 6 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/779.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/779/head:pull/779

PR: https://git.openjdk.java.net/jfx/pull/779