RFR: 8242489: ChoiceBox: initially toggle not sync'ed to selection

[Kevin Rushforth]

On Mon, 13 Apr 2020 10:36:51 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

> Macroscopic issue is that initially, the toggle is not sync'ed to the selection state. Root reason is an missing else
> block when updating toggle selection state (see report for details).
> Fixed by introducing the else block and removing all follow-up errors that tried to amend the consequences of the
> incorrect selection state
> - removed listener to selected item
> - removed toggle selection update in showing listener
> 
> The former also fixed the memory leak when replacing the selectionModel plus an unreported NPE when the selectionModel
> is null initially.
> Added tests that failed before the fix and passed after. As there had been no tests around toggle state, so added some
> to verify that the change doesn't break. Enhanced shim/skin to allow access to popup for testing. Removed the
> informally ignored test part for memory leak.

@aghaisas can you review this?

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PR: https://git.openjdk.java.net/jfx/pull/177