RFR: 8353599: TabPaneSkin: add 'menuGraphicFactory' property [v2]

[Andy Goryachev]

> Tries to address the mystery of missing graphic in the TabPane overflow menu.
> For a quick tester, use https://bugs.openjdk.org/secure/attachment/114240/TabPaneGraphicFactoryExample.java
> 
> # Overflow Menu Graphic Property in the TabPaneSkin
> 
> Andy Goryachev
> 
> <andy.goryachev at oracle.com>
> 
> 
> ## Summary
> 
> Introduce a `menuGraphicFactory` property in the `TabPaneSkin` class eliminates the current limitation of this skin
> in supporting menu item graphics other than an `ImageView` or `Label` with an `ImageView` graphic.
> 
> 
> 
> ## Goals
> 
> The goals of this proposal are:
> 
> - to allow the application developers to customize the overflow menu items' graphic
> - retain the backward compatibility with the existing application code
> - clarify the behavior of the skin when the property is null (i.e. the current behavior)
> 
> 
> 
> ## Non-Goals
> 
> The following are not the goals of this proposal:
> 
> - disable the overflow menu
> - configure overflow menu graphic property via CSS
> - add this property to the `TabPane` control itself
> 
> 
> 
> ## Motivation
> 
> The existing `TabPaneSkin` does not allow the overflow menu to show graphic other than
> an `ImageView` or `Label` with an `ImageView`.
> 
> This limitation makes it impossible for the application developer to use other graphic Nodes,
> such as `Path` or `Canvas`, or in fact any other types.  The situation becomes even more egregious
> when the tabs in the `TabPane` have no text.
> 
> Example:
> 
> 
> public class TabPaneGraphicFactoryExample {
>     public void example() {
>         Tab tab1 = new Tab("Tab1");
>         tab1.setGraphic(createGraphic(tab1));
> 
>         Tab tab2 = new Tab("Tab2");
>         tab2.setGraphic(createGraphic(tab2));
> 
>         TabPane tabPane = new TabPane();
>         tabPane.getTabs().addAll(tab1, tab2);
> 
>         TabPaneSkin skin = new TabPaneSkin(tabPane);
>         // set overflow menu factory with the same method as was used to create the tabs
>         skin.setMenuGraphicFactory(this::createGraphic);
>         tabPane.setSkin(skin);
>     }
> 
>     // creates graphic Nodes for tabs as well as the overflow menu
>     private Node createGraphic(Tab tab) {
>         switch (tab.getText()) {
>         case "Tab1":
>             return new Circle(10);
>         case "Tab2":
>             return new Canvas(10, 10);
>         default:
>             return null;
>         }
>     }
> }
> 
> 
> 
> ## Description
> 
> The proposed solution adds the `menuGraphicFactory` property in the `TabPaneSkin` class:
> 
> 
>     /**
>      * This property allows to control the graphic for the overflow menu items,
>      * by genera...

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - popup menu on demand
 - Merge remote-tracking branch 'origin/master' into 8353599.menu.factory
 - Merge remote-tracking branch 'origin/master' into 8353599.menu.factory
 - javadoc
 - Merge remote-tracking branch 'origin/master' into 8353599.menu.factory
 - graphic factory

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1773/files
  - new: https://git.openjdk.org/jfx/pull/1773/files/e50a550a..7cb4fa8e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1773&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1773&range=00-01

  Stats: 472 lines in 15 files changed: 162 ins; 173 del; 137 mod
  Patch: https://git.openjdk.org/jfx/pull/1773.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1773/head:pull/1773

PR: https://git.openjdk.org/jfx/pull/1773