RFR: 8314906: [testbug] Create behavior tests for text input controls [v2]

[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.

Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:

  win

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1221/files
  - new: https://git.openjdk.org/jfx/pull/1221/files/db657f76..440c2b4e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1221&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1221&range=00-01

  Stats: 52 lines in 1 file changed: 2 ins; 38 del; 12 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