RFR: 8294156: Allow PassFailJFrame.Builder to create test UI [v4]

[Alexey Ivanov]

> This enhances the `Builder` pattern added in [JDK-8294535](https://bugs.openjdk.org/browse/JDK-8294535) with a new method `testUI` which allows passing a lambda expression or a method reference to create *the test UI window*.
> 
> The `PassFailJFrame` will automatically call the method on the EDT to create the UI, add it to the internal list of windows, install the window closing listener and finally position and show both the instructions and test UI.
> 
> Alternatively, you can pass an already created window.
> 
> The `main` method of a manual test could look as simple as a sequence of calls:
> 
> 
>     public static void main(String[] args) throws Exception {
>         PassFailJFrame.builder()
>                       .instructions(INSTRUCTIONS)
>                       .testUI(() -> createTestUI())
>                       .build()
>                       .awaitAndCheck();
>     }
> 
> where `createTestUI` returns a test UI window.

Alexey Ivanov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 16 commits:

 - Merge master
 - Add instructions on how to use PassFailJFrame
 - 8294156: Allow creating several test windows
   
   The windows can be positioned in advance, or
   a call back PositionWindows interface can be used
   to define their positions after the instruction UI
   frame is positioned on the screen.
 - Remove trailing whitespace
 - Mark the Builder class final
   
   It's not supposed to be extended.
 - Amend message in window closing handler
   
   The WindowClosingHandler is used both for the instruction
   frame and for test UI windows.
   Also add blank lines to separate different parts of the class.
 - Use invokeOnEDT in getInstructionFrameBounds
 - Use functional style for disposing of windows
   
   Also clean up the doc for disposeWindows().
 - Use statically imported invokeAndWait and isEDT
 - Build functional test UI
   
   The Builder now provides a method to create test UI,
   PassFailJFrame automatically invokes the method reference
   on the EDT and then shows both the instruction frame and
   the test window.
 - ... and 6 more: https://git.openjdk.org/jdk/compare/14090ef6...eff09d0d

-------------

Changes: https://git.openjdk.org/jdk/pull/15665/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15665&range=03
  Stats: 442 lines in 1 file changed: 365 ins; 38 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/15665.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15665/head:pull/15665

PR: https://git.openjdk.org/jdk/pull/15665