Add external_name to account.move.line_ids view

We need to display the field as invisible here although it
is already defined on invoice_line_ids tree above. Having it
defined only there would only set the external_name key with its
value inside the invoice_line_ids key of the values dictionary
that is passed to create function. However, this invoice_line_ids
key is popped in account.move._move_autocomplete_invoice_lines_create
function to keep only the line_ids to create the account.move and
avoid duplicated account.move.line records.

account_move_line_accounting_description/views/account_move.xml

@@ -17,6 +17,18 @@
             <xpath expr="//field[@name='invoice_line_ids']//form" position="inside">
                 <field name="external_name" />
             </xpath>
+            <!--
+            WARNING: We need to display the field as invisible here although it
+             is already defined on invoice_line_ids tree above. Having it
+             defined only there would only set the external_name key with its
+             value inside the invoice_line_ids key of the values dictionary
+             that is passed to create function. However, this invoice_line_ids
+             key is popped in account.move._move_autocomplete_invoice_lines_create
+             function to keep only the line_ids to create the account.move and
+             avoid duplicated account.move.line records. -->
+            <xpath expr="//field[@name='line_ids']//tree" position="inside">
+                <field name="external_name" invisible="1" />
+            </xpath>
         </field>
     </record>
 </odoo>