Prepares the text for processing.
Filters should not use the prepare method for anything other than escaping, because that would short-circuit the control the user has over the order in which filters are applied.
string $text: The text string to be filtered.
string $langcode: The language code of the text to be filtered.
bool $cache: A Boolean indicating whether the filtered text is going to be cached in {cache_filter}.
string $cache_id: The ID of the filtered text in {cache_filter}, if $cache is TRUE.
string The prepared, escaped text.
public function prepare($text, $langcode, $cache, $cache_id);