[IMP] mail: introduce ComposerSuggestable model

This will allow to remove AND/OR mix in identifying fields of composer
suggestion view.

Part of task-2741982

closes odoo/odoo#94999

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/src/models/thread.js

@@ -2257,6 +2257,13 @@ registerModel({
         serverMessageUnreadCounter: attr({
             default: 0,
         }),
+        suggestable: one('ComposerSuggestable', {
+            default: insertAndReplace(),
+            inverse: 'thread',
+            isCausal: true,
+            readonly: true,
+            required: true,
+        }),
         /**
          * Determines the `SuggestedRecipientInfo` concerning `this`.
          */