message_post and various mail.thread related code still support a thread_model
context key allowing to redirect message post on another model. Purpose of
this commit is to get rid of that context key and support model / res_id
fields coming from either the record on which we run, either parameters of
message_post. Indeed those parameter match the one used as fields on mail
message. It makes sense to support them for customization if necessary
instead of using a context key.
This context key exists since a lot of time. It is difficult to find the
source as history is quite complex when the mail was refactored in 2012.
See notably 6aa4f80b2d and 2c4ed841b9 for example.
Thibault Delavallée
324ae5ed8f