[Turbofan] Cleanup: move SerializerForBackgroundCompilation to .cc

It's sufficient to expose a run function and flags.

Bug: v8:7790
Change-Id: I956a545ddce9e469e6a6196a4b63d9e3a119526d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1706469
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62774}

src/compiler/pipeline.cc

@@ -1367,10 +1367,9 @@ struct SerializationPhase {
       flags |=
           SerializerForBackgroundCompilationFlag::kAnalyzeEnvironmentLiveness;
     }
-    SerializerForBackgroundCompilation serializer(
-        data->broker(), data->dependencies(), temp_zone,
-        data->info()->closure(), flags, data->info()->osr_offset());
-    serializer.Run();
+    RunSerializerForBackgroundCompilation(data->broker(), data->dependencies(),
+                                          temp_zone, data->info()->closure(),
+                                          flags, data->info()->osr_offset());
   }
 };