[ExecuTorch] Separate extension.Module Namespaces from Aten and non-Aten

Pull Request resolved: pytorch/executorch#10576

# Context

Separate `extension.Module` Namespaces to be `executorch::extension::module` and `executorch::extension::module::aten`, otherwise if a package relies on both aten and non-aten of the same implementation and the namespace is the same, there will be duplicate symbol issue like:

```
ld.lld: error: duplicate symbol: vtable for executorch::extension::Module
>>> defined at {redacted}/executorch/extension/module/__module__/__stripped__/module.cpp.pic.stripped.o:(vtable for executorch::extension::Module)
>>> defined at {redacted}/executorch/extension/module/__module_aten__/__stripped__/module.cpp.pic.stripped.o:
```

# Proposal

Doing something similar to what we already did for `bundled_program` in pytorch/executorch#10307

Since `extension.Module` is a public API, we introduce a namespace alias, so that existing use cases won't get affected. Since namespace alias doesn't create additional symbols, there won't be duplicate symbol issue.

ghstack-source-id: 282066740
@exported-using-ghexport

Differential Revision: [D73903870](https://our.internmc.facebook.com/intern/diff/D73903870/)

Author: zhenyan-zhang-meta

extension/module/bundled_module.cpp

@@ -15,6 +15,7 @@
 
 namespace executorch {
 namespace extension {
+namespace ET_BUNDLED_MODULE_NAMESPACE {
 
 namespace {
 std::unique_ptr<BufferDataLoader> program_data_loader(
@@ -108,5 +109,6 @@ runtime::Error BundledModule::verify_method_outputs(
       *method, bundled_program_ptr_, testset_idx, rtol, atol);
 }
 
+} // namespace ET_BUNDLED_MODULE_NAMESPACE
 } // namespace extension
 } // namespace executorch

extension/module/bundled_module.h

@@ -10,8 +10,15 @@
 
 #include <executorch/extension/module/module.h>
 
+#ifdef USE_ATEN_LIB
+#define ET_BUNDLED_MODULE_NAMESPACE bundled_module::aten
+#else // !USE_ATEN_LIB
+#define ET_BUNDLED_MODULE_NAMESPACE bundled_module
+#endif // USE_ATEN_LIB
+
 namespace executorch {
 namespace extension {
+namespace ET_BUNDLED_MODULE_NAMESPACE {
 
 using executorch::extension::ET_MODULE_NAMESPACE::Module;
 
@@ -121,5 +128,6 @@ class BundledModule : public Module {
   bool is_loaded_from_file_ = false;
 };
 
+} // namespace ET_BUNDLED_MODULE_NAMESPACE
 } // namespace extension
 } // namespace executorch

extension/module/module.h

@@ -16,6 +16,12 @@
 
 #include <executorch/runtime/executor/program.h>
 
+#ifdef USE_ATEN_LIB
+#define ET_MODULE_NAMESPACE module::aten
+#else // !USE_ATEN_LIB
+#define ET_MODULE_NAMESPACE module
+#endif // USE_ATEN_LIB
+
 namespace executorch {
 namespace extension {
 
@@ -24,6 +30,10 @@ using ET_RUNTIME_NAMESPACE::MethodMeta;
 using ET_RUNTIME_NAMESPACE::NamedDataMap;
 using ET_RUNTIME_NAMESPACE::Program;
 
+class ExecuTorchJni;
+
+namespace ET_MODULE_NAMESPACE {
+
 /**
  * A facade class for loading programs and executing methods within them.
  */
@@ -493,16 +503,24 @@ class Module {
  protected:
   std::unordered_map<std::string, MethodHolder> methods_;
 
-  friend class ExecuTorchJni;
+  friend class executorch::extension::ExecuTorchJni;
 };
 
+} // namespace ET_MODULE_NAMESPACE
 } // namespace extension
 } // namespace executorch
 
 namespace torch {
 namespace executor {
 // TODO(T197294990): Remove these deprecated aliases once all users have moved
 // to the new `::executorch` namespaces.
-using ::executorch::extension::Module;
+using ::executorch::extension::ET_MODULE_NAMESPACE::Module;
 } // namespace executor
 } // namespace torch
+
+namespace executorch {
+namespace extension {
+// backward compatible namespace alias
+using ::executorch::extension::ET_MODULE_NAMESPACE::Module;
+} // namespace extension
+} // namespace executorch

extension/module/test/bundled_module_test.cpp

@@ -11,6 +11,7 @@
 
 using namespace ::executorch::extension;
 using namespace ::executorch::runtime;
+using namespace ::executorch::extension::ET_BUNDLED_MODULE_NAMESPACE;
 
 class BundledModuleTest : public ::testing::Test {
  protected: