Problem/Motivation
The test filter plugin in core/modules/filter/tests/filter_test/lib/Drupal/filter_test/Plugin/Filter/FilterTestReplace.php uses the wrong case for getPluginId():
<?php
$text[] = 'Filter: '. $this->getLabel() . ' ('. $this->getPluginID() . ')';
?>While function names are (apparently) not case sensitive in PHP (@alexpott looked this up) and "Id" is a different word from "ID", we should nonetheless use the same case as the method defined on PluginBase.
Proposed resolution
Rename FilterTestReplace::getPluginID() to getPluginId().
