RFR: 8273743: KeyCharacterCombination for "+" does not work on US QWERTY keyboard layout

[Martin Fox]

The algorithm in `KeyCharacterCombination.match` relies on the call `Toolkit.getKeyCodeForChar` which is difficult to implement correctly. It defies the way most keyboard API’s work and no platform has got it right yet. In particular the Mac and Linux implementations have to resort to a brute-force approach which monitors keystrokes to learn the relationship between keys and characters.

This PR introduces an alternative mechanism which directly asks the platform whether a given key can generate a specific character. It also allows the platform to attach identifying key information to each KeyEvent to make it easier to answer the question (much, much easier).

This is mostly dumb plumbing. On the front-end there’s a new call `View.notifyKeyEx` that takes an additional platform-specific `hardwareCode` parameter. It also returns a boolean indicating whether the event was consumed or not so I can fix JDK-8087863. If you want to follow the path visit the files in this order:

	View.java
	GlassViewEventHandler.java
	TKSceneListener.java
	Scene.java

The `KeyEvent` class has been expanded with an additional `hardwareCode` member that can only be accessed internally. See KeyEvent.java and KeyEventHelper.java.

On the back-end `KeyCharacterCombination.match` calls a new routine `Toolkit.getKeyCanGenerateCharacter` which unpacks the `KeyEvent` information and sends it on to the Application. The default implementation falls back to the old `getKeyCodeForChar` call but platform specific Applications can send it on to the native glass code.

	KeyCharacterCombination.java
	Toolkit.java
	QuantumToolkit.java
	Application.java
	GtkApplication.java

The glass code can use the `hardwareCode` to answer the question directly. It also has enough information to fall back on the old `getKeyCodeForChar` logic while also enabling the keypad (a common complaint is that Ctrl+’+’ only works on the main keyboard and not the keypad, see JDK-8090275).

This PR improves the situation for key events generated by keystrokes. Manually constructed key events won’t work any better or worse than they already do. Based on the bug database I don't think this is an issue.

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Commit messages:
 - New KeyCharacterCombination implementation

Changes: https://git.openjdk.java.net/jfx/pull/694/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=694&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273743
  Stats: 290 lines in 16 files changed: 243 ins; 10 del; 37 mod
  Patch: https://git.openjdk.java.net/jfx/pull/694.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/694/head:pull/694

PR: https://git.openjdk.java.net/jfx/pull/694