add CallControl#setMuteState impl

previously, there was no way to mute a Transactional call via the
CallControl object.  In order to mute the call, the AudioService
was needed.

Now, clients can use CallControl#setMuteState to mute the call.

Fixes: 310669304
Test: 1 new CTS test
Change-Id: I878655c990fc80590339a5d6996f1bf0f9040247
diff --git a/flags/telecom_api_flags.aconfig b/flags/telecom_api_flags.aconfig
index 74cb447..36f20d8 100644
--- a/flags/telecom_api_flags.aconfig
+++ b/flags/telecom_api_flags.aconfig
@@ -27,3 +27,11 @@
   description: "The key is used for dialer apps to mark missed calls as read when it gets the notification on reboot."
   bug: "292597423"
 }
+
+
+flag{
+  name: "set_mute_state"
+  namespace: "telecom"
+  description: "transactional calls need the ability to mute the call audio input"
+  bug: "310669304"
+}