[bug] `SeparatedColumn` throws error

[Matěj Žídek]

Let's say you have list:

  final myList = <String>['hello', 'dog', 'launch'];

and you pass it to SeparatedColumn / SeparatedRow, it throws error:

SeparatedColumn(
    separatorBuilder: () => SizedBox(height: 12),
    children: myList.map((e) => Text('$e\n')).toList(), // Throws error SeparatedColumn: type 'SizedBox' is not a subtype of type 'Text' of 'element'.
  )

This, however builds fine:

SeparatedColumn(
    separatorBuilder: () => SizedBox(height: 12),
    children: [
      ...myList.map((e) => Text('$e\n')),
    ],
  )

Not sure the building process in the Flutter framework but I've the fix. My guess it was modifying the original list which was used somewhere while building so I'm copying it. I've added a test for it.