RFR: 8305925: Add concatenated list view

[Kevin Rushforth]

On Wed, 12 Apr 2023 07:24:08 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> The JavaFX collections framework offers the `FXCollections.concat(ObservableList...)` method, which creates a new modifiable list that contains a concatenated snapshot of the source lists, backed by an `ArrayList`. However, when the source lists are changed, the concatenated list is not updated.
> 
> This PR adds `FXCollections.concatenatedObservableList(ObservableList...)`, which creates an _unmodifiable collection view_ onto the source lists that represents the concatenation of all source elements. When any of the source lists are changed, the change is also reflected in the concatenated view.

Moving to Draft since we haven't finished the discussion of whether we want this feature at this time, and what form it should take.

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PR Comment: https://git.openjdk.org/jfx/pull/1087#issuecomment-1505760283