RFR: 8340308: PassFailJFrame: Make rows default to number of lines in instructions

[Alexey Ivanov]

It has become quite common to use the following code


.rows((int) INSTRUCTIONS.lines().count() + 1)


to set the number of rows for `PassFailJFrame`.

Make this the default value. Newer tests could drop `.rows` from builder configuration if the new default works well.

If a test needs customising the new default value, the newly added method `rowsAdd` could be used to increase the number of rows.

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Commit messages:
 - Add description for Builder.columns method
 - 8340308: PassFailJFrame: Make rows default to number of lines in instructions

Changes: https://git.openjdk.org/jdk/pull/21039/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21039&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340308
  Stats: 35 lines in 1 file changed: 34 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21039.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21039/head:pull/21039

PR: https://git.openjdk.org/jdk/pull/21039