[CFE] add --updateExpectations to coverage suite

So running `pkg/front_end/test/coverage_suite.dart --updateExpectations`
will update `pkg/front_end/test/coverage_suite_expected.dart` and a `git
diff` will give an overview of what changed.

Also save both number of hits and number of misses in the
"expect-file". If nothing else it will give some context
about what has changed.

Also cleanup json coverage output to be sorted and not
include "misses" that are also "hits" (the VM can give
this information).

Change-Id: I426681dde3d4d2ad0a9a7dfa474292c699223d68
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/370520
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Jens Johansen <[email protected]>

pkg/front_end/test/coverage_helper.dart

@@ -203,14 +203,16 @@ class FileCoverage {
 
   Map<String, Object?> toJson() {
     List<int> notCompiledRanges = [];
-    for (var pair in notCompiled) {
+    for (var pair in notCompiled.toList()
+      ..sort((a, b) => a.startPos.compareTo(b.startPos))) {
       notCompiledRanges.add(pair.startPos);
       notCompiledRanges.add(pair.endPos);
     }
+    misses.removeAll(hits);
     return {
       "uri": uri.toString(),
-      "hits": hits.toList(),
-      "misses": misses.toList(),
+      "hits": hits.toList()..sort(),
+      "misses": misses.toList()..sort(),
       "notCompiledRanges": notCompiledRanges,
     };
   }