TPH needs internal isolates

Change the TPH API so that it uses v8::internal::Isolate rather
than v8::isolate.

The third party heap is within the internal namespace and ultimately
needs access to v8::internal::Isolate to do things such as adding code
ranges.  There's no reason for it to use v8:Isolate.

Bug: v8:9533
Change-Id: I8c3ecd6278081f03133013d4e3b02fb3ed228baf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2036088Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Steve Blackburn <steveblackburn@google.com>
Cr-Commit-Position: refs/heads/master@{#66113}

src/heap/heap.cc

@@ -5046,8 +5046,7 @@ void Heap::SetUp() {
 #endif
 
 #ifdef V8_ENABLE_THIRD_PARTY_HEAP
-  tp_heap_ =
-      third_party_heap::Heap::New(reinterpret_cast<v8::Isolate*>(isolate()));
+  tp_heap_ = third_party_heap::Heap::New(isolate());
 #endif
 
   // Initialize heap spaces and initial maps and objects.

src/heap/third-party/heap-api.h

@@ -14,9 +14,9 @@ namespace third_party_heap {
 
 class Heap {
  public:
-  static std::unique_ptr<Heap> New(v8::Isolate* isolate);
+  static std::unique_ptr<Heap> New(v8::internal::Isolate* isolate);
 
-  static v8::Isolate* GetIsolate(Address address);
+  static v8::internal::Isolate* GetIsolate(Address address);
 
   AllocationResult Allocate(size_t size_in_bytes, AllocationType type,
                             AllocationAlignment align);