RFR: 8185886: Improve scrolling performance of TableView and TreeTableView [v2]

[yosbits]

On Sat, 18 Apr 2020 17:40:30 GMT, yosbits <github.com+7517141+yososs at openjdk.org> wrote:

>> My name is "Naohiro Yoshimoto"
>> I have received an approved email on 2019-8-3.
>
> 19fabf2eafcb02b519d39a1b0a9dad5b9209db64
> 
> * Constructor creates multiple cell nodes, but the
> Fixed a wasteful problem of creating all cells and deleting out-of-display cells because the fixedCellSize attribute
> was not initialized in the constructor..
> * Reduce the load on ExpressionHelper.removeListener by removing cells outside of the display range from the back of the
>   scrolling operation.

When setting the cell height to a fixed value with setFixedCellSize(), column virtualization can improve performance.

As the next step, I think it is possible to try to enable column virtualization regardless of whether
setFixedCellSize() is set or not. Before doing this step, the direct access validation of the internal structure of the
test code needs to be changed via the public API.

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PR: https://git.openjdk.java.net/jfx/pull/125