[CFE] Add --traceStepTiming to strong and weak suite

This option traces in which steps time is spent when running a suite.

On my machine for instance I get these results on a run ofstrong and
weak suites:

$ out/ReleaseX64/dart --enable-asserts pkg/front_end/test/fasta/strong_suite.dart -DsemiFuzz=true --traceStepTiming
Running suite strong...
[ 02:58 | 100.0% | +  571 | -    0 ]: strong/value_class/value_mixin_error

             check errors: 0:00:00.156828 ms
stress constant evaluator: 0:00:00.269382 ms
                    print: 0:00:00.439196 ms
                typeCheck: 0:00:02.575744 ms
       match expectations: 0:00:04.869435 ms
                   verify: 0:00:04.951524 ms
                  compile: 0:00:18.307246 ms
      transform component: 0:00:22.121665 ms
                 semifuzz: 0:00:59.717862 ms
              write .dill: 0:01:05.066461 ms
                      run: 0:01:15.028423 ms

$ out/ReleaseX64/dart --enable-asserts pkg/front_end/test/fasta/weak_suite.dart -DsemiFuzz=true --traceStepTiming
Running suite weak...
[ 10:11 | 100.0% | + 2225 | -    0 ]: weak/variance/unconstrained_inference

             check errors: 0:00:00.506722 ms
stress constant evaluator: 0:00:00.759073 ms
                    print: 0:00:01.293962 ms
                typeCheck: 0:00:09.974299 ms
       match expectations: 0:00:16.386842 ms
                   verify: 0:00:17.585821 ms
                  compile: 0:01:01.966016 ms
      transform component: 0:01:23.560216 ms
                 semifuzz: 0:02:50.969460 ms
              write .dill: 0:04:08.087519 ms
                      run: 0:05:17.911549 ms

In both cases writing dill and running takes quite a while, and
interesting writing the dill is almost as slow as running it.

Change-Id: Ie528e8f7e8a493e17e40a7235b456cc75381ca61
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/242874
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>