RFR: 8341560: Better documentation for KeyCombinations/KeyCodes/KeyEvents

[Martin Fox]

Updated documentation for various topics related to keyboard handling.

This documentation deprecates the KP_UP, KP_DOWN, KP_LEFT, and KP_RIGHT key codes. As outlined in JDK-8316307 no platform has ever generated these codes and using them with a Robot will produce inconsistent results.

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Commit messages:
 - Spacing fix and wording change.
 - Merge remote-tracking branch 'upstream/master' into shortcutdocs
 - Further wording updates.
 - Merge remote-tracking branch 'upstream/master' into shortcutdocs
 - More wording changes.
 - Merge remote-tracking branch 'upstream/master' into shortcutdocs
 - Merge remote-tracking branch 'upstream/master' into shortcutdocs
 - More wording tweaks.
 - Merge remote-tracking branch 'upstream/master' into shortcutdocs
 - More work on wording
 - ... and 2 more: https://git.openjdk.org/jfx/compare/f7b563c7...53594042

Changes: https://git.openjdk.org/jfx/pull/2036/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=2036&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341560
  Stats: 49 lines in 4 files changed: 33 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jfx/pull/2036.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2036/head:pull/2036

PR: https://git.openjdk.org/jfx/pull/2036