bufferhubd: Add DetachedBufferChannel

1/ Introduces four new BufferHub RPC operations.
2/ Implements the ProducerBufferDetach with test case.
3/ Also fixes a bug that Hangup signal wasn't propogated to the client
   when bufferhubd closes a producer channel.

Bug: 38137191
Bug: 70046255
Bug: 70912269
Test: buffer_hub-test
Change-Id: Ia2ba0e95abd3c1b960670c505c6fdb9c9de3a6dd
diff --git a/services/vr/bufferhubd/Android.bp b/services/vr/bufferhubd/Android.bp
index 6009a95..6122846 100644
--- a/services/vr/bufferhubd/Android.bp
+++ b/services/vr/bufferhubd/Android.bp
@@ -17,6 +17,7 @@
     "bufferhubd.cpp",
     "consumer_channel.cpp",
     "producer_channel.cpp",
+    "detached_buffer_channel.cpp",
     "consumer_queue_channel.cpp",
     "producer_queue_channel.cpp",
 ]