Reland "[vm] Fix V8 snapshot profile handling of the dispatch table."

This is a reland of 5909fd111d

Does a large refactoring on the V8 snapshot profile writer
to clean things up, add more debugging support, and to fix
the problems that surfaced during the original landing.

Other changes:

Changes Serializer::CreateArtificialNodeIfNeeded() to create
artificial nodes for Code objects and immutable arrays.

Fixes CodeSerializationCluster::Trace() to only push needed parts of
discarded code objects, instead of tracing them like full code objects.

Adds test cases to v8_snapshot_profile_writer_test that exercise
the following situations (both separately and together):

* Non-symbolic stack traces are enabled and code and function objects
  are dropped when not needed at runtime.

* Creation of the dispatch table is disabled.

TEST=vm/dart{,_2}/v8_snapshot_profile_writer_test

Original change's description:
> [vm] Fix V8 snapshot profile handling of the dispatch table.
>
> Fixes https://github.com/dart-lang/sdk/issues/45702.
>
> TEST=Tests listed in the issue above.
>
> Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try
> Change-Id: Ibf5e3ccf3828c01f9dda47de360314dabe8cb8a9
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/195272
> Reviewed-by: Daco Harkes <dacoharkes@google.com>
> Commit-Queue: Tess Strickland <sstrickl@google.com>

Change-Id: I8e7030267fe190079a8f68d00fe20bf7170e5719
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-mac-release-simarm64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-obfuscate-linux-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/195513
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>

pkg/expect/lib/expect.dart

@@ -168,6 +168,15 @@ class Expect {
     _fail("Expect.isNotNull(actual: <$actual>$msg) fails.");
   }
 
+  /**
+   * Checks whether the Iterable [actual] is empty.
+   */
+  static void isEmpty(Iterable actual, [String reason = ""]) {
+    if (actual.isEmpty) return;
+    String msg = _getMessage(reason);
+    _fail("Expect.isEmpty(actual: <$actual>$msg) fails.");
+  }
+
   /**
    * Checks whether the expected and actual values are identical
    * (using `identical`).