Fix destructor for EmbedderStateScope

EmbedderState is forward declared in public header for
EmbedderStateScope. Default std::unique_ptr's destructor needs a fully
defined class. Defining default destructor in implementation file fixes
this.

Bug: chromium:1263871
Change-Id: I8ccc58f56a758927dc5d7a39387188185e7d3827
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3338697
Auto-Submit: Corentin Pescheloche <cpescheloche@fb.com>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78363}

include/v8-embedder-state-scope.h

@@ -32,6 +32,8 @@ class V8_EXPORT EmbedderStateScope {
   EmbedderStateScope(Isolate* isolate, Local<v8::Context> context,
                      EmbedderStateTag tag);
 
+  ~EmbedderStateScope();
+
  private:
   // Declaring operator new and delete as deleted is not spec compliant.
   // Therefore declare them private instead to disable dynamic alloc

src/api/api.cc

@@ -10366,6 +10366,11 @@ EmbedderStateScope::EmbedderStateScope(Isolate* isolate,
                                        EmbedderStateTag tag)
     : embedder_state_(new internal::EmbedderState(isolate, context, tag)) {}
 
+// std::unique_ptr's destructor is not compatible with Forward declared
+// EmbedderState class.
+// Default destructor must be defined in implementation file.
+EmbedderStateScope::~EmbedderStateScope() = default;
+
 void TracedReferenceBase::CheckValue() const {
 #ifdef V8_HOST_ARCH_64_BIT
   if (!val_) return;