In this commit some reorganization is performed within mail compose message code. Purpose is to reorder a bit methods by main usage: onchange, CRUD, actions, values generation with rendering and template management. Some renaming is performed on action methods, notably send_mail that has some impact on sub-addons. Finally we also set onchange and sub-onchange methods private. No functional change should be implied by this commit. LINKS Task ID-2377974 Community PR odoo/odoo#61467 Enterprise PR odoo/enterprise#14633