Implement facets as views filter (in a new major version)

Problem/Motivation

Facets filters queries (views and others) and manages the filter information in query parameters, with facet blocks replacing the filter form.
Note that facets support views queries and others (like search).

This makes integration into views difficult (the corresponding issue #2957950: Add views area plugin does not implement a filter, it only displays facet blocks in a views area).
Also folks want filter-form-like functionality like in #2811331: Create a multiple select dropdown widget.

Let's discuss if going views-filter-plugin may be a win in the end.

Proposed resolution

Add "facets as views filter plugin" as a second option beneath "facets from facet blocks".
Drop all ajax support in facets, for views it's built in.
Consider dropping support for non-views usage.