translation_entity_entity_insert() assumes entity IDs are integers

Problem/Motivation

translation_entity.module keeps track of entity translations in its {translation_entity} table. For each translation it stores the entity ID, which it accesses by EntityInterface::id(), and tries to do so in a field of type 'int'. ContentEntities are fine with that, but ConfigEntities return their machine name, which results in a fatal SQL error, when it tries to save an entity translation along the lines of

Error message
Drupal\Core\Database\DatabaseExceptionWrapper: SQLSTATE[HY000]: General error: 1366 Incorrect integer value

In order to reproduce this, turn on entity_translation.module and then in a second step turn on contact.module. That tries to save the default contact category and BOOM!

I filed this as major, it might be considered critical, but I didn't want to piss people off, and this should be a rather easy one anyway, so...

Proposed resolution

Change the SQL field to type 'varchar'.

Remaining tasks

Write tests. I don't think we need either an upgrade path or upgrade path tests.

User interface changes

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API changes

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