[jfx16] RFR: 8252389: Fix mistakes in FX API docs

Fri Jan 29 16:23:41 UTC 2021

On Fri, 29 Jan 2021 13:20:38 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> The usual doc fixes (for OpenJFX 16).
>> 
>> Can wait until RDP2 to see if something else comes up.
>
> @nlisker I'll wait to review this until after you add the fix noted in [JDK-8260430](https://bugs.openjdk.java.net/browse/JDK-8260430).

I added a fix for JDK-8260430. Note that the underlying behavior in this class is different than that of `Node`. While both have a map of properties, `Node` uses a special key to add/get the user data to/from the map while `MenuItem` has a separate field for it. In `Node` these methods are convenience methods, but here they have a separate functionality.

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PR: https://git.openjdk.java.net/jfx/pull/380