[analyzer] Stable analysis tool

Tool the - in my testing at least - is very stable in terms of
instruction counts used as reported by `perf stat`.

Only requires small changes to the analyzer and doesn't affect the part
that's covered by api.txt.

Running it on an extracted dill (with an aot-compiled tool) I get numbers like
this:

```
perf stat -e task-clock:u,cycles:u,instructions:u,branch-misses:u -r3 out/ReleaseX64/dart-sdk/bin/dartaotruntime --deterministic pkg/analyzer/tool/stable_analysis.aot /tmp/extracted_compile_dart_compile
```

```
[...]
50,853,198,745      instructions:u                   #    1.18  insn per cycle              ( +-  0.00% )
[...]
```

Running it 10 times (without `-r3`) I get this:

```
    50,853,237,614      instructions:u                   #    1.18  insn per cycle
    50,853,477,778      instructions:u                   #    1.19  insn per cycle
    50,852,534,741      instructions:u                   #    1.17  insn per cycle
    50,852,728,437      instructions:u                   #    1.18  insn per cycle
    50,853,298,284      instructions:u                   #    1.18  insn per cycle
    50,853,151,431      instructions:u                   #    1.17  insn per cycle
    50,853,754,852      instructions:u                   #    1.18  insn per cycle
    50,852,509,185      instructions:u                   #    1.17  insn per cycle
    50,853,878,495      instructions:u                   #    1.18  insn per cycle
    50,853,437,912      instructions:u                   #    1.18  insn per cycle
```

where the difference between the smallest and the largest number is <0.0027%

Change-Id: I84d616201520a50904854cac06958faf6330468b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/449760
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>