define D-Bus error names corresponding to members of Channel_Text_Send_Error

Submitted by Rohan Garg

Assigned to Telepathy bugs list

Link to original bug (#49398)

Description

Turns out that ReceivedMessage::DeliveryDetails::error provides more specific error messages than ReceivedMessage::DeliveryDetails::dbusError

Hence, the error messages in ChannelTextSendError must be included in the list of error strings in the telepathy-spec so that ReceivedMessage::DeliveryDetails::dbusError provides specific error messages