[FIX] mail: do not eat all document.body.drop event

In fb051d3420 there was some changes on drag and drop of chatter
windows, but this would break the drag and drop of summernote because it
wait for document.drop event for hiding the drop zone.

opw-2259522
closes #51448

closes odoo/odoo#51478

X-original-commit: 4aaf5b1f562f4cd30e05b020741eb936f6e20a20
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>

addons/mail/static/src/js/composers/basic_composer.js

@@ -657,7 +657,6 @@ var BasicComposer = Widget.extend({
      */
     _onBodyFileDrop: function (ev) {
         ev.preventDefault();
-        ev.stopPropagation();
         this.$(".o_file_drop_zone_container").addClass("d-none");
     },
     /**