[IMP] account, hr_expense: add section for attachment preview

An empty div `o_attachment_preview` is added in expense and vendor bills form
views. It will be used as a container to preview the attachment.

The actual behaviour will be implemented in another commit.

Task 40663

addons/account/views/account_invoice_view.xml

@@ -344,6 +344,7 @@
                         </page>
                     </notebook>
                 </sheet>
+                <div class="o_attachment_preview" attrs="{'invisible': ['|',('type', '!=', 'in_invoice'),('state', '!=', 'draft')]}"/>
                 <div class="oe_chatter">
                     <field name="message_follower_ids" widget="mail_followers"/>
                     <field name="activity_ids" widget="mail_activity"/>

addons/hr_expense/views/hr_expense_views.xml

@@ -97,6 +97,7 @@
                         <field name="description" class="oe_inline" placeholder="Notes..."/>
                     </div>
                 </sheet>
+                <div class="o_attachment_preview"/>
                 <div class="oe_chatter">
                     <field name="message_follower_ids" widget="mail_followers"/>
                     <field name="activity_ids" widget="mail_activity"/>