RFR: 8270839: Remove deprecated implementation methods from Scene [v2]

[Ajit Ghaisas]

On Tue, 20 Jul 2021 20:37:17 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> This removes following implementation methods in Scene by making them package-scope. They were previously deprecated for removal by [JDK-8270246](https://bugs.openjdk.java.net/browse/JDK-8270246):
>> 
>> 
>>     public void disposePeer()
>>     public void enableInputMethodEvents(boolean enable)
>>     public void processKeyEvent(KeyEvent e) 
>> 
>> 
>> One of the test harness classes was calling `Scene::processKeyEvent` directly, so I changed it to call it via `SceneHelper`.
>
> Kevin Rushforth has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Export com.sun.javafx.scene to system tests to fix test failure

Marked as reviewed by aghaisas (Reviewer).

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PR: https://git.openjdk.java.net/jfx/pull/579