[FIX] mail: composer expand

The expand arrow hides the last characters of the first line, which many
people (and me in particular) find annoying. We put it at the bottom
instead.

opw-1830762

addons/mail/static/src/less/composer.less

@@ -51,7 +51,7 @@
             border: none;
         }
         .o_composer_button_full_composer {
-            .o-position-absolute(0, 0);
+            .o-position-absolute(auto, 0);
         }
         @media (max-width: @screen-xs-max) {
             .o_composer_button_send {