Refactor setting.Database.UseXXX to methods (#23354)

Replace #23350.

Refactor `setting.Database.UseMySQL` to
`setting.Database.Type.IsMySQL()`.

To avoid mismatching between `Type` and `UseXXX`.

This refactor can fix the bug mentioned in #23350, so it should be
backported.

cmd/dump.go

@@ -279,7 +279,7 @@ func runDump(ctx *cli.Context) error {
 	}()
 
 	targetDBType := ctx.String("database")
-	if len(targetDBType) > 0 && targetDBType != setting.Database.Type {
+	if len(targetDBType) > 0 && targetDBType != setting.Database.Type.String() {
 		log.Info("Dumping database %s => %s...", setting.Database.Type, targetDBType)
 	} else {
 		log.Info("Dumping database...")