src: add way to get IsolateData and allocator from Environment

Add a way to get the current `IsolateData*` and, from it, the current
Node.js `ArrayBufferAllocator` if there is one. This can be useful
for re-using either one of these structures as an embedder.

PR-URL: #36441
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

src/api/environment.cc

@@ -466,6 +466,14 @@ MultiIsolatePlatform* GetMainThreadMultiIsolatePlatform() {
   return per_process::v8_platform.Platform();
 }
 
+IsolateData* GetEnvironmentIsolateData(Environment* env) {
+  return env->isolate_data();
+}
+
+ArrayBufferAllocator* GetArrayBufferAllocator(IsolateData* isolate_data) {
+  return isolate_data->node_allocator();
+}
+
 MultiIsolatePlatform* GetMultiIsolatePlatform(Environment* env) {
   return GetMultiIsolatePlatform(env->isolate_data());
 }

src/node.h

@@ -488,6 +488,8 @@ NODE_EXTERN void DefaultProcessExitHandler(Environment* env, int exit_code);
 
 // This may return nullptr if context is not associated with a Node instance.
 NODE_EXTERN Environment* GetCurrentEnvironment(v8::Local<v8::Context> context);
+NODE_EXTERN IsolateData* GetEnvironmentIsolateData(Environment* env);
+NODE_EXTERN ArrayBufferAllocator* GetArrayBufferAllocator(IsolateData* data);
 
 NODE_EXTERN void OnFatalError(const char* location, const char* message);
 NODE_EXTERN void PromiseRejectCallback(v8::PromiseRejectMessage message);

test/cctest/test_environment.cc

@@ -596,6 +596,9 @@ TEST_F(NodeZeroIsolateTestFixture, CtrlCWithOnlySafeTerminationTest) {
                                           {}),
                   node::FreeEnvironment};
     CHECK(environment);
+    EXPECT_EQ(node::GetEnvironmentIsolateData(environment.get()),
+              isolate_data.get());
+    EXPECT_EQ(node::GetArrayBufferAllocator(isolate_data.get()), nullptr);
 
     v8::Local<v8::Value> main_ret =
         node::LoadEnvironment(environment.get(),