codec_negotiation: Implement outgoing_call_offer_pref

Based on this new endpoint setting, a joint list of preferred codecs
between those received from the Asterisk core (remote), and those
specified in the endpoint's "allow" parameter (local) is created and
is used to create the outgoing SDP offer.

* Add outgoing_call_offer_pref to pjsip_configuration (endpoint)

* Add "call_direction" to res_pjsip_session.

* Update pjsip_session_caps.c to make the functions more generic
  so they could be used for both incoming and outgoing.

* Update ast_sip_session_create_outgoing to create the
  pending_media_state->topology with the results of
  ast_sip_session_create_joint_call_stream().

* The endpoint "preferred_codec_only" option now automatically sets
  AST_SIP_CALL_CODEC_PREF_FIRST in incoming_call_offer_pref.

* A helper function ast_stream_get_format_count() was added to
  streams to return the current count of formats.

ASTERISK-28777

Change-Id: Id4ec0b4a906c2ae5885bf947f101c59059935437

doc/CHANGES-staging/res_pjsip_call_offer_pref.txt

@@ -0,0 +1,8 @@
+Subject: res_pjsip
+Subject: res_pjsip_session
+Master-Only: True
+
+Two new options, incoming_call_offer_pref and outgoing_call_offer_pref
+have been added to res_pjsip endpoints that specify the preferred order
+of codecs to use between those received/sent in an SDP offer and those
+set in the endpoint configuration.

doc/CHANGES-staging/res_pjsip_incoming_call_offer_pref.txt

@@ -1,53 +0,0 @@
-Subject: res_pjsip
-Subject: res_pjsip_session
-Master-Only: True
-
-A new option, incoming_call_offer_pref, was added to res_pjsip endpoints that
-specifies the preferred order of codecs to use between those received in the
-offer, and those set in the configuration.
-
-Valid values include:
-  local - prefer and order by configuration (default).
-  local_single - prefer and order by configuration, but only choose 'top'
-                 most codec
-  remote - prefer and order by incoming sdp.
-  remote_single - prefer and order by incoming sdp, but only choose 'top' most
-                  most codec
-
-Example A:
-  [alice]
-  type=endpoint
-  incoming_call_offer_pref=local
-  allow=!all,opus,alaw,ulaw
-
-  Alice's incoming sdp=g722,ulaw,alaw
-  RESULT: alaw,ulaw
-
-Example B:
-  [alice]
-  type=endpoint
-  incoming_call_offer_pref=local_single
-  allow=!all,opus,alaw,ulaw
-
-  Alice's incoming sdp=g722,ulaw,alaw
-  RESULT: alaw
-
-Example C:
-  [alice]
-  type=endpoint
-  incoming_call_offer_pref=remote
-  allow=!all,opus,alaw,ulaw
-
-  Alice's incoming sdp=g722,ulaw,alaw
-  RESULT: ulaw,alaw
-
-Example D:
-  [alice]
-  type=endpoint
-  incoming_call_offer_pref=remote_single
-  allow=!all,opus,alaw,ulaw
-
-  Alice's incoming sdp=g722,ulaw,alaw
-  RESULT: ulaw
-
-