Refactor dumpBackup.php and dumpTextPass.php to be Maintenance subclasses

Refactor dumpBackup.php and dumpTextPass.php to be Maintenance subclasses

Use the Maintenance class's new $orderedOptions and support for
passing options multiple times. This allows for option "chaining".

The BackupDumper and TextPassDumper class now extend Maintenance, but
should continue to function as before. The public function processArgs()
has been removed and replaced by processOptions(), which takes no
parameters. It is unlikely that users of these classes were calling
processArgs.

Inheritors of these classes that overrode processOption() will now need to
override processOptions() and use Maintenance::getOption() and friends.

The maintenance/backupTextPass.inc file has been deleted. Users should
include maintenance/dumpTextPass.php instead.

Bug: T122587
Change-Id: I2473ee119c185d1b2b00ac4b1e70ee8a6cafe4a3