RATIONALE
Improve usage of composer in comment or email mode: support batch-posting in
comment, support more configuration from templates, improve global model.
SPECIFICATIONS
Support a real res_ids field on mail.compose.message model. Instead of relying
on active_ids from context, store it once for all at composer level and use
it in code. Active_ids usage is still done at default_get level, using it to
populate the field.
Improve usage of domain, renamed to res_domain to match other document related
fields naming. Add support of a res_domain_user_id field allowing to set the
user from which the domain should be evaluated.
Composer now runs on a list of IDs. Mass mail mode and comment mode are now
distinct from running on a singleton or on more records. Rendered or raw
mode is not triggered by
* mass mailing mode: always display raw mode, whatever the number of records;
* comment mode: display rendered mode when having a single record (like the
previous comment mode). Display raw mode when having either no records
either at least two records.
Task-3035101 (Mail: Support batch-posting from composer)
Part-of: odoo/odoo#99482