This commit reverts the functionality introduced in PR #26260
(later refined by #27175, #27190, #27508) in which filtering by
attribute using the layered nav widget was improved to handle the
cases of variations out of stock. The revert is a response to the
numerous problems reported by users in Woo 4.4 and 4.5
Not all the code has been reverted, only the code that resulted in
visible functionality changes. Thus, the code that generates
term relationships for variations is still in place to keep database
consistency and to keep the reverting changes to the minimum needed.
The layered nav filtering doesn't work well with variable products
when some variations have stock and other don't. When a term is
selected in the widget, a variable product having no stock for
the variation corresponding to that term but having stock for
other variations will be displayed, but it shouldn't.
This commit fixes that by introducing two changes:
- A new override of "is_visible" for WC_Product_Variable that
looks at the supplied filters, compares them against the corresponding
available variations and calculates the visibility based on
the query type (OR or AND).
- A hook on the "found_posts" filter in WC_Query, that adjusts
the posts count based on the found products visibility
when there are filters available; this is needed to sync the
"displaying X posts" messages and the paging when variable
products are hidden due to stock status.
Additionally, the visibility calculated in "found_posts" is cached
as loop variables so that it isn't calculated again when actually
displaying the products.