DBStructure enhancements (#5437)

* Adding DBStructure enhancements

- Added DBStructure::rename()
- Added DBStructure::existTable()
- Added DBStructure::existColumn()

(cherry picked from commit 4ae06ec)

* Adding `pre_update_1279` method

- Added DBStructure::rename()
- Added DBStructure::existTable()
- Added DBStructure::existColumn()

(cherry picked from commit 8496d84)

* code standards

(cherry picked from commit 551d09b)

* simplify to `empty` instead `is_null`

(cherry picked from commit ce68835)

src/Database/DBA.php

@@ -644,6 +644,10 @@ class DBA
 
 		$fields = [];
 
+		if (empty($condition)) {
+			return DBStructure::existsTable($table);
+		}
+
 		reset($condition);
 		$first_key = key($condition);
 		if (!is_int($first_key)) {