RFR: 8341235: Improve default instruction frame title in PassFailJFrame

[Alexey Ivanov]

The default title for the instruction frame in `PassFailJFrame` is currently _“Test Instruction Frame”_.

Most tests change this default to _“Test Instructions”_ which describes the content and purpose of the frame better. So, this should be the default title, and it's shorter.

jtreg has a property which describes the test name. Thus, the title could be more specific: _“<testName.java> - Test Instructions”_.

Additionally, I added javadoc comments to the default parameters of `PassFailJFrame` and to the `Builder.validate` method.

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Commit messages:
 - 8341235: Improve default instruction frame title in PassFailJFrame

Changes: https://git.openjdk.org/jdk/pull/21320/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21320&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341235
  Stats: 42 lines in 1 file changed: 39 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/21320.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21320/head:pull/21320

PR: https://git.openjdk.org/jdk/pull/21320