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.cpp b/media/libaudiohal/impl/StreamHalAidl.cpp
index 98c655e..1c15cfb 100644
--- a/media/libaudiohal/impl/StreamHalAidl.cpp
+++ b/media/libaudiohal/impl/StreamHalAidl.cpp
@@ -486,7 +486,7 @@
 }
 
 // static
-::aidl::ConversionResult<::aidl::android::hardware::audio::common::SourceMetadata>
+ConversionResult<::aidl::android::hardware::audio::common::SourceMetadata>
 StreamOutHalAidl::legacy2aidl_SourceMetadata(const StreamOutHalInterface::SourceMetadata& legacy) {
     ::aidl::android::hardware::audio::common::SourceMetadata aidl;
     aidl.tracks = VALUE_OR_RETURN(
@@ -804,7 +804,7 @@
 }
 
 // static
-::aidl::ConversionResult<::aidl::android::hardware::audio::common::SinkMetadata>
+ConversionResult<::aidl::android::hardware::audio::common::SinkMetadata>
 StreamInHalAidl::legacy2aidl_SinkMetadata(const StreamInHalInterface::SinkMetadata& legacy) {
     ::aidl::android::hardware::audio::common::SinkMetadata aidl;
     aidl.tracks = VALUE_OR_RETURN(