drupal_static() won't work with persistent servers or kernel tests

Problem/Motivation

The use of drupal_static() in facets_exposed_filters_get_processed_facet() means that persistent servers won't work.

It also means that using Kernel tests with facets (see https://www.drupal.org/node/3502609) won't work unless tests reset the static cache, which is tricky to debug and figure out.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes