[cleanup] Fix forward declaration ordering in isolate.h

Bug: v8:9396
Change-Id: I0933112bb7e0aa7e4428d057116572723b9e74c4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1706476Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#62776}

src/execution/isolate.h

@@ -91,8 +91,8 @@ class RootVisitor;
 class RuntimeProfiler;
 class SetupIsolateDelegate;
 class Simulator;
-class StartupDeserializer;
 class StandardFrame;
+class StartupDeserializer;
 class StubCache;
 class ThreadManager;
 class ThreadState;