RFR: JDK-8320444: Column drag header is positioned wrong for nested columns [v2]

[Andy Goryachev]

On Tue, 21 Nov 2023 20:03:31 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> When a nested column is dragged, the column drag header (blue) is positioned wrong.
>> It appears at the very left of the table and not where the column is.
>> 
>> ![image](https://github.com/openjdk/jfx/assets/66004280/6c2a0f61-f32d-4c38-9549-e2e20f5bd4f8)
>> 
>> The fix is to calculate the bound based off the `TableHeaderRow` (and not the parent `NestedTableColumnHeader`.
>
> Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve test code.

tested on macOS and windows (the latter with fractional scale).  looks good.

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Marked as reviewed by angorya (Reviewer).

PR Review: https://git.openjdk.org/jfx/pull/1292#pullrequestreview-1743162993