Clear all messages on install

Problem/Motivation

/**
 * Implements hook_install().
 */
function modal_page_install() {
  $messenger = \Drupal::messenger();
  $messenger->deleteAll();
  $messenger->addStatus(
    t('Module <em class="placeholder">Modal Page</em> has been enabled.')
  );
  $messenger->addStatus(t('Thanks for installing Modal Page'));
  $messenger->addStatus(t('You may create Modal by visiting <a href="@url_settings">@url_settings</a>', [
    '@url_settings' => Url::fromRoute('modal_page.default')->toString(),
  ]));
}

Delete all messages can be wrong, because of the Drupal feedback

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet