fix(spp_user_roles): exclude role-backing groups from Groups dropdown

UI-created roles auto-generate backing res.groups records that then
appear in the Groups tab dropdown of other roles. Add domain filter
on implied_ids to exclude groups linked to roles.

Author: emjay0921

spp_user_roles/views/role.xml

@@ -20,6 +20,11 @@
             <xpath expr="//field[@name='name']" position="after">
                 <field name="role_type" />
             </xpath>
+            <xpath expr="//field[@name='implied_ids']" position="attributes">
+                <attribute
+                    name="domain"
+                >[('role_id', '=', False)]</attribute>
+            </xpath>
             <xpath
                 expr="//field[@name='line_ids']/list/field[@name='user_id']"
                 position="attributes"