RFR: 8314906: [testbug] Create behavior tests for text input controls

[Andy Goryachev]

Creating the first batch of tests and testing framework that enables writing behavior tests for javafx controls, focusing on key bindings.  The idea is to make writing such tests a simple process.  

This PR deals with the descendants of TextInputControl (TextField, PasswordField, TextArea).  Most of the tests are headless, but in some cases (TextArea) a headful test is required because the behavior needs rendered text to function (example: page up / page down / line start / line end and the like).

The tests exercise the key bindings registered by the Skin (or, rather the associated Behavior) at least once, and sometimes more than once.

Some mappings cannot be tested due to Robot not supporting keypad events (created [JDK-8316307](https://bugs.openjdk.org/browse/JDK-8316307)).

In addition, the key bindings are documented in /doc-files/behavior markdown documents.

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Commit messages:
 - disabled keypad tests
 - text area tests
 - docs
 - text area doc
 - nbsp
 - text input control doc
 - doc
 - mac bindings
 - test navigation
 - robot test base
 - ... and 22 more: https://git.openjdk.org/jfx/compare/624fe86f...db657f76

Changes: https://git.openjdk.org/jfx/pull/1221/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1221&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314906
  Stats: 2758 lines in 16 files changed: 2721 ins; 23 del; 14 mod
  Patch: https://git.openjdk.org/jfx/pull/1221.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1221/head:pull/1221

PR: https://git.openjdk.org/jfx/pull/1221