Make Filter Products by Stock work with PHP templates

[Aljullu]

Currently, it's not possible to use the Filter Products by Stock block with PHP templates. That's because that block is designed to only work with the All Products block.

This issue is about updating it, so it can work with the Shop catalog template.

Take into account currently there isn’t a widget equivalent, so it might require some changes in WC core in order to get this block working with PHP templates. (That's why the estimate of this issue is higher than the one from similar issues)

To reproduce

1. With a block theme, go to Appearance > Editor > Template > Product Catalog.
2. Add the Filter Products by Stock block above the product grid.
3. Change the selected values in the filter block
4. Notice the products in the product grid don't update.

Expected behavior

The products in the product grid should update based on the selected filters.