emulator: Add HFP 1.6 AG card driver
emulator: Set card driver

If the version is 1.6, send the corresponding card driver name to card
creation. If the version is not 1.6, send NULL.
hfp_ag_bluez5: Send HFP version to card creation

Extract the version from the fd_properties dictionary, if present.
Fallback to HFP version 1.5 if not present.

After that, send it to the card creation.
hfp_ag_bluez5: Register HFP AG version 1.6
emulator: Add Codec Negotiation feature

This commit adds Codec Negotiation to the emulator's list of features.
emulator: Add AT+BAC support

When the emulator receives a AT+BAC SET command, it stores the
available HF codecs.
emulator: Keep information about AT+BAC calls

The AG must only init the codec negociation procedure if the HF has
already sent an AT+BAC command in the current Service Level Connection.
emulator: Respond to AT+BCC command

This commit verifies the conditions where the AT+BCC command will fail.

The codec connection setup is missing.
include: Add g_at_server_register_response()
gatserver: Implement g_at_server_register_response

Certain AT commands only make sense if received in response to another
AT command, and this is especially important when sending unsolicited
commands that receives responses. But there is no mechanism on
gatserver side that allows to implement this behavior.

This commit adds a function which indicates what AT command the
gatserver is expecting. If the next command is not the desired one,
then a ERROR command is sent.
emulator: Setup codec connection

This commit sends an unsolicited +BCS command with the selected codec
when the AG receives with success an AT+BCC command.

Currently the codec is hardcoded to CVSD.
emulator: Receive AT+BCS response

This commit verifies if the codec id sent by HF is the same as
previous sent by AG.
emulator: Setup synchronous connection

After respond OK to AT+BCS, the AG should establish a synchronous
connection with HF.
emulator: Copy callback mechanism from atutil.h

atutil.h needs GAtChat and GAtResult definitions and we do not have
these definitions inside emulator.c.
emulator: Implement AG card .Connect() for HFP 1.6
TEMP: Don't check Card.Connect() D-Bus sender
WIP: test: Add hfp-answer-call-with-sco