fix: Consider all children of TaskGroups in DAGs

[simster7]

Fixes #3739
Fixes #3780

Bug came to be because:

1. Task A is a TaskGroup (i.e. uses withItems, withParams, etc.)
2. Task A's tasks are empty (i.e. withParams: "")
3. Task B depends on Task A
4. Task B is a target task (i.e. it is a leaf task in the DAG)

Since Task A had no expanded tasks, its children were actually normal tasks (Task B) instead of the expected expanded tasks. Since we previously used a "shortcut" by skipping over the expanded tasks (i.e. queuing only the children of children of TaskGroup nodes), we never considered Task B.

Since we can't tell when a TaskGroup's children are expanded tasks or normal tasks, we remove our use of the "shortcut" and always queue all children of TaskGroups. This is not a significant performance hindrance since the unique queue introduced in #3418 is able to handle this case well.

[simster7]

Alternate solution to this in #3746