DownmixProcess: Add tests to validate the downmix process.

Added methods to set and validate parameters.
Added test to verify multichannel to stereo conversion for STRIP type.
Added test to verify multichannel to stereo conversion for FOLD type.

Bug:314953788
Test: atest VtsHalDownmixTargetTest
Change-Id: I31ee4df3eac6ae42e3e3cabebd1622e860581eab
diff --git a/audio/aidl/vts/Android.bp b/audio/aidl/vts/Android.bp
index ad816c7..191f928 100644
--- a/audio/aidl/vts/Android.bp
+++ b/audio/aidl/vts/Android.bp
@@ -86,6 +86,9 @@
     name: "VtsHalDownmixTargetTest",
     defaults: ["VtsHalAudioTargetTestDefaults"],
     srcs: ["VtsHalDownmixTargetTest.cpp"],
+    shared_libs: [
+        "libaudioutils",
+    ],
 }
 
 cc_test {