ICU-22036 Modify ICU4J performance test framework to work when executed by

ICU-22036 Modify ICU4J performance test framework to work when executed by
GitHub Action. This includes introducing a new flag (-a) to indicate
invocation from command line/GHA shell, moving elements of the workflow
from Perl into the Java framework (calculation of iteration numbers), and
generating NDJSON output for GitHub Benchmark processing.
Backward compatibility with the Perl script invocation has been preserved.

ICU-22036 Adds a comment clarifying the reason why NDJSON output is generated.