ProductVariationAttributeMapper::selectVariation() throws for products with mixed variation types

Follow-up to #3635025: ProductVariationAttributeMapper::prepareAttributes() is quadratic in the number of attributes and throws for mixed variation types.

Problem/Motivation

ProductVariationAttributeMapper::selectVariation() calls getAttributeValueId() for every submitted attribute value on every variation. When a product has variations of more than one type, a variation that lacks one of the submitted attribute fields makes getAttributeValueId() throw InvalidArgumentException: Unknown attribute field name. This happens when the add-to-cart form is rebuilt (AJAX attribute change) or submitted.

Proposed resolution

As in #3635025, read each variation's attribute values once with getAttributeValueIds() and compare with $values[$field_name] ?? NULL, stopping at the first mismatch. A variation without an attribute is treated as not matching it.

Remaining tasks

• Kernel test for mixed variation types.

API changes

None.