Allow spreadsheet migrate sources

Patch has been re rolled on 8.x-1.x-dev based on 8.x-1.1 version and support for extensions xls ods added

Patch has been re rolled on 8.x-1.x-dev based on 8.x-1.2 version. Includes support for xls ods added extensions.

Thanks for the contributions.

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

This introduces a use Drupal\migrate_spreadsheet\Plugin\migrate\source\Spreadsheet; line in MigrateSourceUiForm.php, but does not introduce a dependency on the migrate_spreadsheet module, so PHPStorm complains about an undefined class Spreadsheet.

Also, why does it introduce these changes to .gitlab-ci.yml??

phpcs:
  allow_failure: false
phpstan:
  allow_failure: false
phpstan (next major):
  allow_failure: true
phpstan (next minor):
  allow_failure: true