RFR: 8340461: Amend description for logArea

[Alexey Ivanov]

Resolve the error:

PassFailJFrame.java:161: error: text not allowed in <ul> element
 *     <li>to add a log area</li>,
                                 ^


Shorten the rendered javadoc for `log`, `logClear` and `logSet`.

@azvegint, could you take a look?

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Commit messages:
 - 8340461: Amend description for logArea

Changes: https://git.openjdk.org/jdk/pull/21138/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21138&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340461
  Stats: 9 lines in 1 file changed: 4 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/21138.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21138/head:pull/21138

PR: https://git.openjdk.org/jdk/pull/21138