Schema comparator does not detect renamed foreign keys

[denis-korchagin95]

Q	A
Version	3.10.4, 4.4.3

Summary

The comparator detects renamed columns and renamed indexes, but not renamed foreign keys.
A foreign key that differs from the database only by its name produces no diff, so
schema:update reports the schema as in sync and the old constraint name is never reconciled.

Cause: in Comparator the FK matching loop discards any structurally-equal pair regardless of
name (if (diffForeignKey(...) === false) unset(...)), and diffForeignKey() never compares the
name. There is no detectRenamedForeignKeys() / TableDiff::$renamedForeignKeys (unlike indexes).

Reproduce

use Doctrine\DBAL\Schema\Comparator;
use Doctrine\DBAL\Schema\Table;
use Doctrine\DBAL\Platforms\MySQLPlatform;

function makeTable(string $fkName): Table {
    $t = new Table('widget');
    $t->addColumn('id', 'integer');
    $t->addColumn('reviewed_by', 'integer', ['notnull' => false]);
    $t->setPrimaryKey(['id']);
    $t->addForeignKeyConstraint('account', ['reviewed_by'], ['id'], [], $fkName); // only the NAME differs
    return $t;
}

$platform = new MySQLPlatform();
$diff = (new Comparator($platform))->compareTables(
    makeTable('widget__account_legacy'), // in the database
    makeTable('FK_85F91ED085D7FB47'),    // generated by the mapping
);

var_dump($diff->isEmpty()); // true — no diff produced

Expected vs actual

• Expected: a name-only change is emitted as DROP FOREIGN KEY <old> + ADD CONSTRAINT <new>
  (no platform supports atomic FK rename), as indexes are handled today.
• Actual: isEmpty() === true, no SQL. Changing onDelete instead does surface the FK,
  confirming the gap is name-specific.

Related: #6390, #6445, #7356