Add ability to search product list by SKU

[michaelbromley]

Is your feature request related to a problem? Please describe.
I'm always frustrated when I need to e.g. apply a facet to a product but only know the SKU of one of its variants. I then need to search the variant in the variant list, use the breadcrumbs to access the parent product, then add a facet.

If I want to delete a product knowing only an SKU, I need to do the above, then copy the product name, go back to the product list and paste it, then select it and do the delete.

Describe the solution you'd like
Ability to search by SKU also in the product list, give results where any products have a variant which matches the SKU (using "contains")

[michaelbromley]

Correctly implementing this on the product variant list depends on first supporting more complex boolean filter expressions, as covered in #2594