Declare `ConversionResult` in `android` namespace

Previously the declaration was depending on the `BACKEND_NDK`
define, and `ConversionResult` could end up in the `aidl` NS
(::aidl::ConversionResult). Having it in `android` is more
convenient as it works for nested namespaces of `android`, for
example `android::effect`.

Added alias `aidl::android::ConversionResult` for the NDK
backend case.

Bug: 205884982
Test: m
Change-Id: Ic3238144d35afb86db57d5d620f2f28ccd89021e
Merged-In: Ic3238144d35afb86db57d5d620f2f28ccd89021e
diff --git a/media/libaudiohal/impl/StreamHalAidl.h b/media/libaudiohal/impl/StreamHalAidl.h
index e3cae77..85efb35 100644
--- a/media/libaudiohal/impl/StreamHalAidl.h
+++ b/media/libaudiohal/impl/StreamHalAidl.h
@@ -313,7 +313,7 @@
   private:
     friend class sp<StreamOutHalAidl>;
 
-    static ::aidl::ConversionResult<::aidl::android::hardware::audio::common::SourceMetadata>
+    static ConversionResult<::aidl::android::hardware::audio::common::SourceMetadata>
     legacy2aidl_SourceMetadata(const StreamOutHalInterface::SourceMetadata& legacy);
 
     const std::shared_ptr<::aidl::android::hardware::audio::core::IStreamOut> mStream;
@@ -365,7 +365,7 @@
   private:
     friend class sp<StreamInHalAidl>;
 
-    static ::aidl::ConversionResult<::aidl::android::hardware::audio::common::SinkMetadata>
+    static ConversionResult<::aidl::android::hardware::audio::common::SinkMetadata>
     legacy2aidl_SinkMetadata(const StreamInHalInterface::SinkMetadata& legacy);
 
     const std::shared_ptr<::aidl::android::hardware::audio::core::IStreamIn> mStream;