[FFI][REFACTOR] Cleanup namespace (apache#18280)

* [FFI][REFACTOR] Cleanup namespace

This PR cleansup the namespace to ensure all ffi classes
are accessed through ffi:: namespace.
It will helps to cleanup the ffi package before isolation.

* fix hexagon

Author: tqchen

include/tvm/ffi/cast.h

@@ -73,8 +73,5 @@ inline ObjectPtr<BaseType> GetObjectPtr(ObjectType* ptr) {
   return details::ObjectUnsafe::ObjectPtrFromUnowned<BaseType>(ptr);
 }
 }  // namespace ffi
-
-using ffi::GetObjectPtr;
-using ffi::GetRef;
 }  // namespace tvm
 #endif  // TVM_FFI_CAST_H_

include/tvm/ffi/container/array.h

@@ -1140,7 +1140,5 @@ inline constexpr bool type_contains_v<Array<T>, Array<U>> = type_contains_v<T, U
 }  // namespace details
 
 }  // namespace ffi
-
-using ffi::Array;
 }  // namespace tvm
 #endif  // TVM_FFI_CONTAINER_ARRAY_H_

include/tvm/ffi/container/map.h

@@ -1755,7 +1755,5 @@ inline constexpr bool type_contains_v<Map<K, V>, Map<KU, VU>> =
 }  // namespace details
 
 }  // namespace ffi
-
-using ffi::Map;
 }  // namespace tvm
 #endif  // TVM_FFI_CONTAINER_MAP_H_

include/tvm/ffi/container/variant.h

@@ -298,7 +298,5 @@ template <typename... V, typename T>
 inline constexpr bool type_contains_v<Variant<V...>, T> = (type_contains_v<V, T> || ...);
 }  // namespace details
 }  // namespace ffi
-
-using ffi::Variant;
 }  // namespace tvm
 #endif  // TVM_FFI_CONTAINER_VARIANT_H_

include/tvm/ffi/dtype.h

@@ -38,8 +38,6 @@ namespace ffi {
  * \brief Extension code beyond the DLDataType.
  *
  * This class is always consistent with the DLPack.
- *
- * TODO(tvm-team): update to latest DLPack types.
  */
 enum DLExtDataTypeCode { kDLExtCustomBegin = 129 };
 

include/tvm/ffi/memory.h

@@ -225,7 +225,5 @@ inline ObjectPtr<ArrayType> make_inplace_array_object(size_t num_elems, Args&&..
 }
 
 }  // namespace ffi
-
-using ffi::make_object;
 }  // namespace tvm
 #endif  // TVM_FFI_MEMORY_H_

include/tvm/ffi/optional.h

@@ -410,7 +410,5 @@ class Optional<T, std::enable_if_t<use_ptr_based_optional_v<T>>> : public Object
   }
 };
 }  // namespace ffi
-
-using ffi::Optional;
 }  // namespace tvm
 #endif  // TVM_FFI_OPTIONAL_H_

include/tvm/ffi/string.h

@@ -993,9 +993,6 @@ inline std::ostream& operator<<(std::ostream& out, const String& input) {
 }
 /// \endcond
 }  // namespace ffi
-
-using ffi::Bytes;
-using ffi::String;
 }  // namespace tvm
 
 /// \cond Doxygen_Suppress