RFR: JDK-8186188: TableColumHeader: initial auto-size broken if has graphic [v6]

[Marius Hanl]

> This PR fixes the issue that the initial column autosizing is wrong under some circumstances.
> The following things will break the initial autosizing:
> - Bold Column text (that is where I initially found this problem)
> - Another font / font size
> - Graphic
> 
> The reason is actually quite simple: The CSS is not (yet) applied initially, we therefore ALWAYS take the default font into account + the graphic is not yet layouted as well.
> 
> _It was not so easy to write tests for this, also for me the `test_resizeColumnToFitContentHeader` is always failing locally. I don't know what happens here, but he seems to not find a (Stub?) `Font` for me._
> **EDIT: Found out the cause and fixed it. I will check if I can write more tests since it works now. :)**
> 
> The test I wrote now is checking if the css is applied after we triggered the autosize, which is what we would expect here since we measure text.
> 
> I also copied the `TableColumnHeaderTest` and rewrote the tests for `TreeTableView` as well, so we can catch any errors here as well since they both use different code (although it is technically the same - C&P errors can happen very easy).

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

  improve tests + JUnit 5 for new test

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1405/files
  - new: https://git.openjdk.org/jfx/pull/1405/files/53acbc5c..b4d03d44

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1405&range=05
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1405&range=04-05

  Stats: 78 lines in 2 files changed: 32 ins; 16 del; 30 mod
  Patch: https://git.openjdk.org/jfx/pull/1405.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1405/head:pull/1405

PR: https://git.openjdk.org/jfx/pull/1405