`getForeignKeys()` - inconsistency of array keys

[arogachev]

SQLite:

[['auth_item', 'child' => 'name'], ['auth_item', 'parent' => 'name']];

MySQL:

['auth_item_child_ibfk_1' => ['auth_item', 'child' => 'name'], 'auth_item_child_ibfk_2' => ['auth_item', 'parent' => 'name']];

[samdark]

Do you mean that SQLite does not return FK names?

[arogachev]

I mean integer and string keys difference. Maybe add docs for now.

[vjik]

Foreign key in MySQL supports index name, and in SQLite don't supports, so in SQLite used integer ID (seems, it's just number in order) as name.

I think improve phpdoc and make more specified psalm type for TableSchemaInterface::getForeignKeys() result will be enough.

[Tigrov]

Decided to use ForeignKeyConstraint[] instead of arrays. Related with #734