src: add ability to look up platform based on Environment*

This should eventually remove any necessity to use the global-state
`GetMainThreadMultiIsolatePlatform()`.

Backport-PR-URL: #35241
PR-URL: #30467
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

src/api/environment.cc

@@ -474,6 +474,14 @@ MultiIsolatePlatform* GetMainThreadMultiIsolatePlatform() {
   return per_process::v8_platform.Platform();
 }
 
+MultiIsolatePlatform* GetMultiIsolatePlatform(Environment* env) {
+  return GetMultiIsolatePlatform(env->isolate_data());
+}
+
+MultiIsolatePlatform* GetMultiIsolatePlatform(IsolateData* env) {
+  return env->platform();
+}
+
 MultiIsolatePlatform* CreatePlatform(
     int thread_pool_size,
     node::tracing::TracingController* tracing_controller) {

src/node.h

@@ -456,9 +456,14 @@ NODE_EXTERN void FreeEnvironment(Environment* env);
 NODE_EXTERN Environment* GetCurrentEnvironment(v8::Local<v8::Context> context);
 
 // This returns the MultiIsolatePlatform used in the main thread of Node.js.
-// If NODE_USE_V8_PLATFORM haven't been defined when Node.js was built,
+// If NODE_USE_V8_PLATFORM has not been defined when Node.js was built,
 // it returns nullptr.
+// TODO(addaleax): Deprecate in favour of GetMultiIsolatePlatform().
 NODE_EXTERN MultiIsolatePlatform* GetMainThreadMultiIsolatePlatform();
+// This returns the MultiIsolatePlatform used for an Environment or IsolateData
+// instance, if one exists.
+NODE_EXTERN MultiIsolatePlatform* GetMultiIsolatePlatform(Environment* env);
+NODE_EXTERN MultiIsolatePlatform* GetMultiIsolatePlatform(IsolateData* env);
 
 // Legacy variants of MultiIsolatePlatform::Create().
 NODE_EXTERN MultiIsolatePlatform* CreatePlatform(