Backport:
- https://github.com/odoo/odoo/pull/236489
- https://github.com/odoo/odoo/pull/249086
- https://github.com/odoo/odoo/pull/255497

Task: 6041826

Implemented a new product import system that supports grouping product
variants under a single product template based on the product name.

This new feature allows the creation and update of product templates and
their variants from a single Excel file.

Grouping Logic:
- Variants are grouped onto a product template if they share the same
product name in the import file.

Attribute Value Handling:
- Attribute values are provided in a structured format:
`attribute name:value name`, separated by commas (e.g., Color:Red, Size:M).
- Attributes and their values are automatically created if they do not
already exist in the system.

External ID Handling:
- If a product/variant has attribute values, the external ID is expected
  to be a `product.product` External ID.
- Otherwise (if it's a simple product or the template record), the
  external ID is expected to be a `product.template` External ID.

Example (.csv):

External ID;Internal Reference;Name;Product Type;Barcode;Sales Price;Weight;Sales Description;Attribute values
product_template_1;;T-shirt Big Bang;Goods;;110;;T-shirt with Big Bang Theme;
product_product_1;T-SHIRT-BB-1;T-shirt Big Bang;;code-b-1;;0,12;;Color:Red,Size:S
product_product_2;T-SHIRT-BB-2;T-shirt Big Bang;;code-b-2;;0,13;;Color:Red,Size:M
product_product_3;T-SHIRT-BB-3;T-shirt Big Bang;;;115;0,14;;Color:Blue,Size:L
product_product_4;T-SHIRT-BB-4;T-shirt Big Bang;;;125;0,15;;Size:M,Color:Red
product_product_5;T-SHIRT-SW-RS;T-shirt Stars Wars;Goods;code-1;100;0,12;T-shirt with Stars Wars Theme;Color:Red,Size:S
product_product_6;T-SHIRT-SW-RM;T-shirt Stars Wars;Goods;code-2;100;0,13;T-shirt with Stars Wars Theme;Color:Red,Size:M
product_product_7;T-SHIRT-SW-RL;T-shirt Stars Wars;Goods;code-3;100;0,14;T-shirt with Stars Wars Theme;Color:Red,Size:L
product_product_8;T-SHIRT-SW-BS;T-shirt Stars Wars;Goods;code-5;110;0,12;T-shirt with Stars Wars Theme;Color:Blue,Size:S
product_product_9;T-SHIRT-SW-BM;T-shirt Stars Wars;Goods;code-6;110;0,13;T-shirt with Stars Wars Theme;Color:Blue,Size:M
product_product_10;T-SHIRT-SW-BL;T-shirt Stars Wars;Goods;code-7;110;0,14;T-shirt with Stars Wars Theme;Color:Blue,Size:L

Forward-Port-Of: odoo/odoo#254323