Provide layouts for multiple test UI in PassFailJFrame

JDK-8294156 allows creating and adding multiple test UI frames as part of PassFailJFrame. As mentioned in the code review [1], the framework should provide a few simple layout managers to position the test UI.

The demos [2] for the testUI feature provide implementations which need to be refined.

A quote from the demo layouts [3]:

“I didn't even think about not providing any default implementations of positionTestUI — that's the idea! The framework should support simple layouts.

“Implementing common layouts each time they're used would be a waste of time.

“A method reference to an implementation in PassFailJFrame could be passed. Alternatively, we can add helper methods to builder which selects the Position and positionTestUI.

“The code in TwoWindowsHH.java and TwoWindowsHV.java needs refining. Yet it's a great foundation.”


[1] https://github.com/openjdk/jdk/pull/15665#discussion_r1323491246
[2] https://github.com/openjdk/jdk/pull/15721
[3] https://github.com/openjdk/jdk/pull/15721#discussion_r1326082796