RFR: 8342524: Use latch in AbstractButton/bug6298940.java instead of delay

[Sergey Bylokhov]

On Fri, 24 Jan 2025 16:47:42 GMT, Alexey Ivanov <aivanov at openjdk.org> wrote:

> Use a `CountDownLatch` in `javax/swing/AbstractButton/bug6298940.java` instead of delay.  
> Use `Util.hitMnemonics` instead of custom code to handle macOS.
> 
> I ran the updated test a few times with `JTREG=REPEAT_COUNT=20`, the test always passed in the CI.

test/jdk/javax/swing/AbstractButton/bug6298940.java line 86:

> 84:             }
> 85:         } finally {
> 86:             SwingUtilities.invokeAndWait(() -> frame.dispose());

Usually we follow a pattern to check the frame for null.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23301#discussion_r1933035733