[FIX] mail: keep attachments when switching between note and message

Start a message mail (respectively note) in the chatter. Attach a file.
Switch to note (respectively mail). The attachment is lost.

With this commit, we keep the attachments after the switch.

opw 1925588

closes odoo/odoo#30197

addons/mail/static/src/js/chatter.js

@@ -155,6 +155,7 @@ var Chatter = Widget.extend(chat_mixin, {
             record_name: this.record_name,
             default_body: old_composer && old_composer.$input && old_composer.$input.val(),
             default_mention_selections: old_composer && old_composer.mention_get_listener_selections(),
+            attachment_ids: (old_composer && old_composer.get('attachment_ids')) || [],
         });
         this.composer.on('input_focused', this, function () {
             this.composer.mention_set_prefetched_partners(this.mentionSuggestions || []);

addons/mail/static/src/js/composer.js

@@ -389,7 +389,7 @@ var BasicComposer = Widget.extend(chat_mixin, {
         // Attachments
         this.AttachmentDataSet = new data.DataSetSearch(this, 'ir.attachment', this.context);
         this.fileupload_id = _.uniqueId('o_chat_fileupload');
-        this.set('attachment_ids', []);
+        this.set('attachment_ids', options.attachment_ids || []);
 
         // Mention
         this.mention_manager = new MentionManager(this);
@@ -449,6 +449,7 @@ var BasicComposer = Widget.extend(chat_mixin, {
         dom.autoresize(this.$input, {parent: this, min_height: this.options.input_min_height});
 
         // Attachments
+        this.render_attachments();
         $(window).on(this.fileupload_id, this.on_attachment_loaded);
         this.on("change:attachment_ids", this, this.render_attachments);