MDL-72723 logs: Add get_events_select_exists to the sql_reader interface

- Updates to log stores and backup helper to improve performance when
  checking if a course has been modified.
- This is a breaking change as it adds a new function on the sql_reader
  interface.

Co-authored-by: Kevin Pham <[email protected]>

lib/classes/log/sql_reader.php

@@ -60,6 +60,16 @@ interface sql_reader extends reader {
      */
     public function get_events_select_count($selectwhere, array $params);
 
+    /**
+     * Get whether events are present for the given select clause.
+     *
+     * @param string $selectwhere select conditions.
+     * @param array $params params.
+     *
+     * @return bool Whether events available for the given conditions
+     */
+    public function get_events_select_exists(string $selectwhere, array $params): bool;
+
     /**
      * Fetch records using the given criteria returning an traversable list of events.
      *