Fixes #5584: `yii\rbac\DbRbacManager` should not delete items when deleting a rule on a database not supporting cascade update

Fixes #5435: Added extra checks to `yii\rbac\DbManager` to prevent database exceptions when `$userId` is empty

close #5348

fixes #5119

Fixes #4489: RBAC PhpManager wasn't saving multiple assignmentsFixes #4489: RBAC PhpManager wasn't saving multiple assignments properly

MSSQL syntax fix

- Data is now stored in three separate files for items, assignments and rules. File format is simpler.
- Removed `authFile`. Added `itemsFile`, `assignmentsFile` and `rulesFile`.
- `createdAt` and `updatedAt` are now properly filled with corresponding file modification time.
- `save()` and `load()` are now protected instead of public.
- Added unit test for saving and loading data.

Replaced `clearAll()` and `clearAllAssignments()` in `yii\rbac\ManagerInterface` with `removeAll()`, `removeAllRoles()`, `removeAllPermissions()`, `removeAllRules()` and `removeAllAssignments()`