Refactor Plugin\Filter\MarkdownAlterationsFilter into an event and multiple event subscribers

[Ambient-Impact]

drupal-omnipedia-content/src/Plugin/Filter/MarkdownAlterationsFilter.php

Line 52 in ce0fa3d

class MarkdownAlterationsFilter extends FilterBase implements ContainerFactoryPluginInterface {

Right now, this is a bit of a dumping ground for anything that needs to be done after all Markdown has been rendered. If possible, refactor all of these methods as separate event subscribers, preferably subscribed to a CommonMark event rather than an input filter.