Deprecate usage of Connection::getDriverClass for 'Install\Tasks'

Simple change. It's not worth adding a convenience method in Connection in this case, since the Tasks class gets instantiated directly without connection by the installation routines. Could think of a static method, but that would be a bigger change.

All code changes look good.
Just one more class added to the conditional deprecation of Connection::getDriverClass
For me it is RTBC.

The following text needs to be added to the CR:

The replacement for the database class "Install\Tasks" is:

// Before
$class = Database::getConnection()->getDriverClass('Install\\Tasks');

// Replacement
$class = Database::getConnection()->getConnectionOptions()['namespace'] . '\\Install\\Tasks';

Committed e807300 and pushed to 11.x. Thanks!

mondrake → closed merge request !4427

Updated the CR.

Automatically closed - issue fixed for 2 weeks with no activity.