hook_filter_info() is a hook for defining a set of callbacks that effectively map to a single object
That's almost the definition of what our plugins are. Let's convert it!
None now that #1779026: Convert Text Formats to Configuration System is in
User interface changes
Replaced with \Drupal\filter\Plugin\filter\filter\FilterInterface:
filter_get_filters() (Previously used in conjunction with a format's filter, now the information is stored directly on the filter)