[IMP] stock_account: add product category for SVL groupby

Adds the storage of the product's `categ_id` in the stock valuation
layer as it is a prerequisite for being able to use a groupby in the
tree view.

Part of task-3218314

Part-of: odoo/odoo#119381

addons/stock_account/models/stock_valuation_layer.py

@@ -16,7 +16,7 @@ class StockValuationLayer(models.Model):
 
     company_id = fields.Many2one('res.company', 'Company', readonly=True, required=True)
     product_id = fields.Many2one('product.product', 'Product', readonly=True, required=True, check_company=True, auto_join=True)
-    categ_id = fields.Many2one('product.category', related='product_id.categ_id')
+    categ_id = fields.Many2one('product.category', related='product_id.categ_id', store=True)
     product_tmpl_id = fields.Many2one('product.template', related='product_id.product_tmpl_id')
     quantity = fields.Float('Quantity', readonly=True, digits='Product Unit of Measure')
     uom_id = fields.Many2one(related='product_id.uom_id', readonly=True, required=True)

addons/stock_account/views/stock_valuation_layer_views.xml

@@ -110,6 +110,7 @@
                 <filter string="Has Remaining Qty" name="has_remaining_qty" domain="[('remaining_qty', '>', 0)]"/>
                 <group expand='0' string='Group by...'>
                     <filter string='Product' name="group_by_product_id" context="{'group_by': 'product_id'}"/>
+                    <filter string='Product Category' name="group_by_categ_id" context="{'group_by': 'categ_id'}"/>
                 </group>
             </search>
         </field>