Implement PUSH_BLANK_BUFFERS_ON_STOP in Codec2

PUSH_BLANK_BUFFERS_ON_STOP is a MediaCodec feature that instructs a
codec to display a blank frame at end of playback on codecs configured
with an output surface.

The feature has existed for a while and been implemented for OMX-based
codecs, but it was missing from the newer Codec2-based codecs.

Test: atest DecoderPushBlankBuffersOnStopTest#testPushBlankBuffersOnStopAvc
Bug: 210587592
Change-Id: I3ec3117e991224134cb6cb6b6a601e063e96be26
diff --git a/media/codec2/sfplugin/CCodecConfig.cpp b/media/codec2/sfplugin/CCodecConfig.cpp
index 242eeaf..e486ef0 100644
--- a/media/codec2/sfplugin/CCodecConfig.cpp
+++ b/media/codec2/sfplugin/CCodecConfig.cpp
@@ -324,7 +324,8 @@
     : mInputFormat(new AMessage),
       mOutputFormat(new AMessage),
       mUsingSurface(false),
-      mTunneled(false) { }
+      mTunneled(false),
+      mPushBlankBuffersOnStop(false) { }
 
 void CCodecConfig::initializeStandardParams() {
     typedef Domain D;
@@ -960,8 +961,6 @@
         .limitTo(D::ENCODER & D::VIDEO & D::READ));
 
     /* still to do
-    constexpr char KEY_PUSH_BLANK_BUFFERS_ON_STOP[] = "push-blank-buffers-on-shutdown";
-
        not yet used by MediaCodec, but defined as MediaFormat
     KEY_AUDIO_SESSION_ID // we use "audio-hw-sync"
     KEY_OUTPUT_REORDER_DEPTH