Doublecheck settings being merged

Relocated from #3531327-5: Create new "power user" flag to disable warnings and validation → :

public function settingsForm(array $form, FormStateInterface $form_state): array {
    $this->settings = array_replace_recursive($this->defaultSettings(), $this->settings);

The fact that defaultSettings() are only merged in settingsForm(), and not in the constructor or process(), feels off. That said, it might be 100% valid. I'm thinking that if the filter ever processes text without the form being loaded first, it could result in unexpected behavior? I wonder if it makes more sense to initialize $this->settings in the constructor.