Add AMediaFormat functions to clear and copy

Also move NdkMediaFormat internals to libmedia to avoid a future circular
dependency between libmedia and libmediandk.

Bug: 111407253
Test: build, boot, play some files

Change-Id: I54d91439f216c3834726e5505afef40dc0d93e67
diff --git a/media/libmedia/Android.bp b/media/libmedia/Android.bp
index e6d6b3e..9fe9ee5 100644
--- a/media/libmedia/Android.bp
+++ b/media/libmedia/Android.bp
@@ -191,6 +191,7 @@
         "MediaResourcePolicy.cpp",
         "Visualizer.cpp",
         "StringArray.cpp",
+        "NdkMediaFormatPriv.cpp",
     ],
 
     aidl: {