Replace MySQL-specific GROUP_CONCAT configuration

Problem/Motivation

The BabelService currently uses a MySQL-specific SQL command

$this->db->query("SET SESSION group_concat_max_len = 1000000;");

It violates Drupal's database abstraction principles.

Apart from that using very long IDs in UI and exported files, composed by concatenating the plugin ID and the translation ID looks bad.

Proposed resolution

• TranslationTypePluginInterface::getStrings() to return array to be keyed by hash instead of long concatenated list of plugin:id.
• Use the hash as row ID (data-babel-row) in form and
• Use the hash as translation ID in spreadsheet.
• On retrieving and saving get the plugins and their translation IDs from the tables.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

TranslationTypePluginInterface::getStrings() to return array to be keyed by hash instead of long concatenated list of plugin:id