RFR: 8245575: Show the ContextMenu of input controls with long press gesture on iOS

[Jose Pereda]

This PR uses iOS long press gesture to generate a menu event that will trigger a `ContextMenuEvent`.

Based on this event, input controls will show the ContextMenu (once JDK-8245499 is fixed), and if required, a developer
could add an event handler based on `ContextMenuEvent.CONTEXT_MENU_REQUESTED` for custom processing of such event.

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Commit messages:
 - Use iOS long press gesture to generate a menu event

Changes: https://git.openjdk.java.net/jfx/pull/232/files
 Webrev: https://webrevs.openjdk.java.net/jfx/232/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8245575
  Stats: 32 lines in 3 files changed: 32 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/232.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/232/head:pull/232

PR: https://git.openjdk.java.net/jfx/pull/232