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

[Andy Goryachev]

On Mon, 20 Nov 2023 22:24:58 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`.

the fix looks good, tested with and without nested columns.

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PR Comment: https://git.openjdk.org/jfx/pull/1292#issuecomment-1821405042