Allow users to configure the locale chunk size in settings.php

Problem/Motivation

In 📌 Use a transaction PoDatabaseWriter to improve performance Active it was suggested that we make the chunk size in \locale_translate_batch_import() configurable in settings.php to allow for further performance optimisations.

Proposed resolution

Change the code to something like:

'chunk_size' => \Drupal\Core\Site\Settings::get('locale.chunk_size', 200),

Drupal\Core\Site\Settings should use a use statment and not FQCN.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet