Reland "[compiler] Move InternalizedString to kNeverSerialized"

This is a reland of 04cdcd5a

Got reverted in https://crrev.com/c/v8/v8/+/2534294 due to
TSAN issues. Those are solved in https://crrev.com/c/v8/v8/+/2537693.

Original change's description:
> [compiler] Move InternalizedString to kNeverSerialized
>
> Bug: v8:7790
> Change-Id: I8311b1f4b8239d0688a4b9b9057d6082942bbc00
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2534471
> Reviewed-by: Georg Neis <neis@chromium.org>
> Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71159}

Bug: v8:7790
Change-Id: I95d68e23e4bc81399bcdcf7ce2fdcf49ddfb66c5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2536641
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71180}

src/compiler/heap-refs.h

@@ -61,6 +61,8 @@ enum class OddballType : uint8_t {
   /* Subtypes of FixedArray */                      \
   V(ObjectBoilerplateDescription)                   \
   V(ScopeInfo)                                      \
+  /* Subtypes of String */                          \
+  V(InternalizedString)                             \
   /* Subtypes of Name */                            \
   V(Symbol)                                         \
   /* Subtypes of HeapObject */                      \
@@ -92,7 +94,6 @@ enum class OddballType : uint8_t {
   V(FixedArray)                               \
   V(FixedDoubleArray)                         \
   /* Subtypes of Name */                      \
-  V(InternalizedString)                       \
   V(String)                                   \
   /* Subtypes of JSReceiver */                \
   V(JSObject)                                 \

src/compiler/js-heap-broker.cc

@@ -870,12 +870,10 @@ StringData::StringData(JSHeapBroker* broker, ObjectData** storage,
 class InternalizedStringData : public StringData {
  public:
   InternalizedStringData(JSHeapBroker* broker, ObjectData** storage,
-                         Handle<InternalizedString> object);
-
-  uint32_t array_index() const { return array_index_; }
-
- private:
-  uint32_t array_index_;
+                         Handle<InternalizedString> object)
+      : StringData(broker, storage, object) {
+    DCHECK(!FLAG_turbo_direct_heap_access);
+  }
 };
 
 ObjectData* StringData::GetCharAsString(JSHeapBroker* broker, uint32_t index,
@@ -898,11 +896,6 @@ ObjectData* StringData::GetCharAsString(JSHeapBroker* broker, uint32_t index,
   return result;
 }
 
-InternalizedStringData::InternalizedStringData(
-    JSHeapBroker* broker, ObjectData** storage,
-    Handle<InternalizedString> object)
-    : StringData(broker, storage, object) {}
-
 namespace {
 
 bool IsFastLiteralHelper(Handle<JSObject> boilerplate, int max_depth,