All drop-down config field now support tokens

Drop-down config fields for condition and action plugins in ECA now also support tokens. Other modules can adopt that behaviour by following this small guide. There are a couple of steps to take:

Build config form

Add the following property to the select field, that should support tokens:

    '#eca_token_select_option' => TRUE,

Use the PluginFormTrait

Add the use statement to the plugin class:

  use PluginFormTrait;

Retrieve configuration value

When retrieving the configuration value, e.g. in access, execute or evaluate methods, then a token replacement may be required:

      $field_name = $this->configuration['field_name'];
      if ($field_name === '_eca_token') {
        $field_name = $this->getTokenValue('field_name', 'default');
      }