[IMP] stock: improve warehouses placeholder in route

On `stock.route`, when `warehouse_selectable=True` and
no `warehouse_ids` is set, it applies to every warehouse.
Therefore, the placeholder was adapted to "All Warehouses" for clarity.

Task:4721271

closes odoo#214760

Signed-off-by: Tiffany Chang (tic) <[email protected]>

Author: abyo-odoo

addons/stock/views/stock_location_views.xml

@@ -217,7 +217,7 @@
                             <div class="o_row">
                                 <field name="warehouse_selectable" class="oe_inline" nolabel="1"/>
                                 <field name="warehouse_domain_ids" invisible="1"/>
-                                <field name="warehouse_ids" widget="many2many_tags" class="o_field_highlighted" placeholder="e.g. Central Warehouse" nolabel="1" invisible="not warehouse_selectable"/>
+                                <field name="warehouse_ids" widget="many2many_tags" class="o_field_highlighted" placeholder="All Warehouses" nolabel="1" invisible="not warehouse_selectable"/>
                             </div>
                         </group>
                     </group>