Add conflict resolution for auto-generated FK constraint names

[dereuromark]

Summary

I feel like when we now auto generate them instead of the db, we should do this, as there could be conflict somewhere along the migrations.

• When auto-generating FK constraint names, check if the name already exists
• Append counter suffix (_2, _3, etc.) if a conflict is detected
• Prevents duplicate constraint name errors in edge cases

UPDATE:
Also now respects technical max length limit per constraint using truncate.
We could also add hashing instead of just truncate + counter suffix.

This builds on #1041 which added auto-generation of FK constraint names.

Example

// First FK: generates "articles_user_id"
$table->addForeignKey('user_id', 'users', 'id');

// Second FK on same column (unusual but possible): generates "articles_user_id_2"
$table->addForeignKey('user_id', 'admins', 'id');

Changes

All 4 adapters updated with getUniqueForeignKeyName() method:

• MysqlAdapter
• SqliteAdapter
• PostgresAdapter
• SqlserverAdapter

[dereuromark]

Should the common code by moved to Util class? Regarding the

public static function generateUniqueConstraintName(                                                     
      string $baseName,                                                                                    
      array $existingNames,                                                                                
      int $maxLength                                                                                       
  ): string        

[dereuromark]

@markstory I would squash-merge this first into the open PR, then we can merge the whole thing squashed for easier up/down merges.