parser/gotest: Improve gotest output handling

The reportBuilder has been updated to use the ordered output collector
to keep track of go test output. This makes it possible to include
benchmark output in the generated report and makes sure that output is
preserved when deleting subtest parents from the report.

parser/gotest/report_builder_test.go

@@ -43,7 +43,8 @@ func TestGroupBenchmarksByName(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		got := groupBenchmarksByName(test.in)
+		b := newReportBuilder()
+		got := b.groupBenchmarksByName(test.in)
 		if diff := cmp.Diff(test.want, got); diff != "" {
 			t.Errorf("groupBenchmarksByName result incorrect, diff (-want, +got):\n%s\n", diff)
 		}