Remove set|getOption from Facet Entity et al. and fix schema

After a quick look at the patch, I found this:

1. +++ b/src/Entity/Facet.php
   @@ -306,7 +304,7 @@ class Facet extends ConfigEntityBase implements FacetInterface {
   -      $processor_settings = $this->getOption('processors', []);
   +      $processor_settings =       $processors_settings = !empty($this->processor_configs) ? $this->processor_configs : [];
   

   There's 2 $processor_settings here.

I'll take a look in more detail later.

1. +++ b/config/schema/facets.processor.schema.yml
   @@ -40,3 +40,11 @@ plugin.plugin_configuration.facets_processor.count_limit:
   +# There are no settings intended. So probably always an empty array.
   

   There are no settings intended for this, this will probably always be an empty array but not having a schema available means the facet config is not correct. This is important because the tests use strict config validation.

2. +++ b/src/Entity/Facet.php
   @@ -306,7 +304,7 @@ class Facet extends ConfigEntityBase implements FacetInterface {
   -      $processor_settings = $this->getOption('processors', []);
   +      $processor_settings = !empty($this->processor_configs) ? $this->processor_configs : [];
   

   Looks great.

3. +++ b/src/FacetInterface.php
   @@ -230,6 +183,14 @@ interface FacetInterface extends ConfigEntityInterface {
   +   * Set the query operator.
   

   From the docs: https://www.drupal.org/coding-standards/docs

   Summary lines must start with a third person singular present tense verb, and they must explain what the function does. Example: "Calculates the maximum weight for a list."

   This should be Sets the query operator.

   This is a rule that I tend to forget myself as well ;)

Otherwise this patch is looking great, hopefully the testbot agrees.

fixes test.

Fixed my own remarks from #16.

Tests are green, happy with the code. Thanks for the patches!