WooCommmerce Nested Category Layout 1.20.1

Fix - Ensure that WooCommerce attribute filters would work consistently with the nested category layout template

* Tweak - Do not display categories that have no products in the nested category content template
* Fix - Ensure to use `remove_action` instead of `remove_filter` with `woocommerce_product_query`
* Fix - Bail from applying filters in the main search query
* Fix - Suppress the WooCommerce loop template on pages managed by the plugin to avoid empty HTML elements
* Misc - Code hardening and improvements
* Dev - Add new actions and filters, and update filter parameters in the main nested category content template

Misc - Add compatibility for WooCommerce High Performance Order Storage (HPOS)

* Fix - Improve compatibility with WP filters

* Misc - Require PHP 7.4 and WordPress 5.6