vfs: restore isSea as function, align modules/ with upstream

Restore isSea as a C++ function (was incorrectly changed to a boolean
property), fixing cctest failures where helpers.js calls isSea().
Align all files under lib/internal/modules/ with upstream/main so
VFS introduces zero changes to the module loader internals.

Author: mcollina

lib/internal/main/embedding.js

@@ -13,10 +13,11 @@ const {
   prepareMainThreadExecution,
 } = require('internal/process/pre_execution');
 const {
-  isSea: isLoadingSea,
+  isSea,
   isVfsEnabled: isVfsEnabledFlag,
   isExperimentalSeaWarningNeeded,
 } = internalBinding('sea');
+const isLoadingSea = isSea();
 const { emitExperimentalWarning } = require('internal/util');
 const { emitWarningSync } = require('internal/process/warning');
 const { Module } = require('internal/modules/cjs/loader');

src/node_sea.cc

@@ -259,6 +259,10 @@ SeaResource FindSingleExecutableResource() {
   return sea_resource;
 }
 
+void IsSea(const FunctionCallbackInfo<Value>& args) {
+  args.GetReturnValue().Set(IsSingleExecutable());
+}
+
 void IsExperimentalSeaWarningNeeded(const FunctionCallbackInfo<Value>& args) {
   bool is_building_sea =
       !per_process::cli_options->experimental_sea_config.empty();
@@ -899,27 +903,20 @@ void Initialize(Local<Object> target,
   Environment* env = Environment::GetCurrent(context);
   Isolate* isolate = env->isolate();
 
-  // Set boolean flags as properties (computed once, avoids repeated calls).
-  bool is_sea = IsSingleExecutable();
+  // isVfsEnabled is a boolean property (only used by embedding.js).
   bool is_vfs_enabled = false;
-
-  if (is_sea) {
+  if (IsSingleExecutable()) {
     SeaResource sea_resource = FindSingleExecutableResource();
     is_vfs_enabled =
         static_cast<bool>(sea_resource.flags & SeaFlags::kEnableVfs);
   }
-
-  target
-      ->Set(context,
-            FIXED_ONE_BYTE_STRING(isolate, "isSea"),
-            Boolean::New(isolate, is_sea))
-      .Check();
   target
       ->Set(context,
             FIXED_ONE_BYTE_STRING(isolate, "isVfsEnabled"),
             Boolean::New(isolate, is_vfs_enabled))
       .Check();
 
+  SetMethod(context, target, "isSea", IsSea);
   SetMethod(context,
             target,
             "isExperimentalSeaWarningNeeded",
@@ -929,6 +926,7 @@ void Initialize(Local<Object> target,
 }
 
 void RegisterExternalReferences(ExternalReferenceRegistry* registry) {
+  registry->Register(IsSea);
   registry->Register(IsExperimentalSeaWarningNeeded);
   registry->Register(GetAsset);
   registry->Register(GetAssetKeys);