MDL-53226 search_simpledb: Refine the patch

- Clumsy fallback only when there is no full-text search support
- Mimic solr tests
- pgsql tokenization using simple configuration
- workaround for mysql '*' search issue
- total results proper calculation
- SQL server FTS support
- Standarize dml full-text search checkings
- Upgrade note about the new dml method
- Set search_simpledb as default engine if no solr config

lib/dml/pgsql_native_moodle_database.php

@@ -1497,4 +1497,13 @@ class pgsql_native_moodle_database extends moodle_database {
     private function trim_quotes($str) {
         return trim(trim($str), "'\"");
     }
+
+    /**
+     * Postgresql supports full-text search indexes.
+     *
+     * @return bool
+     */
+    public function is_fulltext_search_supported() {
+        return true;
+    }
 }