RFR: 8087700: [KeyCombination, Mac] One key event sent on Mac versus two on Windows

[Martin Fox]

A KeyCharacterCombination should match a key if the target character is printed on that key. For example, the user should be able to invoke the `Shortcut+'+' ` combination by holding down the Shortcut key and pressing a key that has '+' printed on it. This should work even if '+' is a shifted symbol but the user doesn't hold down the Shift key. 

The Mac implements KeyCharacterCombinations by monitoring keystrokes to discover the relationship between keys and characters. Currently the system only records the character the user typed and no other characters on the same key. This means a shortcut targeting a shifted character may not work until the user types that character using Shift so the system learns the relationship.

This PR keeps the same mechanism in place but always records the shifted and unshifted character for each keystroke.

For the Mac the KeyboardTest app was modified to remove tests for characters accessed using Option. We don't look for these characters because under the hood just about every key has some symbol assigned to the Option modifier that the user probably isn't even aware of. For these character we fall back to the existing logic; once the user types the character it will start working as a shortcut.

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Commit messages:
 - Make KeyCharacterCombinations work reliably on Mac

Changes: https://git.openjdk.org/jfx/pull/1209/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1209&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8087700
  Stats: 46 lines in 2 files changed: 35 ins; 1 del; 10 mod
  Patch: https://git.openjdk.org/jfx/pull/1209.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1209/head:pull/1209

PR: https://git.openjdk.org/jfx/pull/1209