USE declarations must go after the first namespace issue in files with multiple namespaces

Problem/Motivation

For files that have multiple namespaces:

namespace \Drupal\foo\Bar {

  use \Drupal\foo\Baz;

  ...
}

namespace {

  use \Drupal\bar\Biz;

}

The latter use statement throws this error in phpcs:

USE declarations must go after the first namespace declaration

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes