RFR: 8317116: Provide layouts for multiple test UI in PassFailJFrame [v3]

[Alexey Ivanov]

> Provides a set of default layouts for manual test using multiple test UI windows.
> 
> The initial implementation in the demo in #15721 was too complicated. After looking at the simplified version used in #21180, I re-worked the layouts into separate methods.
> 
> The layout methods are in `WindowLayouts` class next to `PassFailJFrame`. It is not necessary to mention it explicitly in the `@build` jtreg tag.
> 
> The builder now provides new methods:
> 
> - `positionTestUIRightRow` positions the test UI windows in a row to the right of the instruction frame. The top of the windows is aligned to that of the instruction frame.
> - `positionTestUIRightColumn` positions the test UI windows in a column to the right of the instruction frame. The top of the first window is aligned to that of the instruction frame.
> - `positionTestUIRightColumnCentered` positions the test UI windows in a column to the right of the instruction frame centering the stack of the windows.
> - `positionTestUIBottomRow` positions the test UI windows in a row to the bottom of the instruction frame. The left of the first window is aligned to that of the instruction frame.
> - `positionTestUIBottomRowCentered` positions the test UI windows in a row to the bottom of the instruction frame centering the row of the windows.
> - `positionTestUIBottomColumn` positions the test UI windows in a column to the bottom of the instruction frame. The left of the first window is aligned to that of the instruction frame.
> 
> If required, the test developer can provide a custom implementation.

Alexey Ivanov has updated the pull request incrementally with two additional commits since the last revision:

 - Remove extra line layoutRow
 - bottomOneRowCentered: layoutColumn -> layoutRow

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21207/files
  - new: https://git.openjdk.org/jdk/pull/21207/files/10c9b563..b4876fde

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21207&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21207&range=01-02

  Stats: 7 lines in 1 file changed: 0 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/21207.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21207/head:pull/21207

PR: https://git.openjdk.org/jdk/pull/21207