ICU-21843 Modifies performance tests and test framework in preparation of

ICU-21843 Modifies performance tests and test framework in preparation of
adding performance tests to ICU CI.
- test/perf/Makefile.in:
    adds strsrchperf to list of subdirs.
    changes target 'all' to compile everything in the standard way.
- test/perf/ustrperf/Makefile.in: changes target executable from stringperf to
  ustrperf (i.e. name of directory) to allow uniform handling with other
  perf tests in GHA CI rules.
- tools/ctestfw/uperf.cpp: changes output to ndjson format for processing with
  GHA Benchmark. Keep the previous output, which gets processed by the Perl
  scripts, when executed in 'verbose' mode. Backward compatibility,
  in case someone still wants to use the Perl scripts for the time being.
  May get cleaned up later.
Also remove a few non-essential output lines that would interfer with
GHA Benchmark.
processing