Allow other loggers than core loggers to FieldDiscovery.php

Problem/Motivation

Loggers can be other things than core's LoggerChannelInterface. For example if you use the monolog library.

Generally we say that loggers are LoggerInterface (from psr/log) in core.

This is not the case for core/modules/migrate_drupal/src/FieldDiscovery.php

This in turn crashes things that invoke this class, when the logger is not set as a LoggerChannel. A typical error would then be:

TypeError: Argument 3 passed to Drupal\migrate_drupal\FieldDiscovery::__construct() must implement interface Drupal\Core\Logger\LoggerChannelInterface, instance of Psr\Log\NullLogger given, called in /my-site/drupal/core/lib/Drupal/Component/DependencyInjection/Container.php on line 277 in Drupal\migrate_drupal\FieldDiscovery->__construct() (line 110 of /my-site/drupal/core/modules/migrate_drupal/src/FieldDiscovery.php).

Proposed resolution

Replace it with LoggerInterface. In fact, in core, this is the only place we specify the type to be LoggerChannelInterface (did a quick search).

Remaining tasks

Create a patch and commit.

User interface changes

None

API changes

Well I guess theoretically, but LoggerChannelInterface extends LoggerInterface

Data model changes

None

Release notes snippet

n/a