refactor: combine elements' container

[Aarebecca]

• 合并元素容器

之前的逻辑中，将节点、边、组合分别置于 3 个 Group，导致元素层级始终固定为：节点 > 边 > 组合
现在将所有元素置于同一个 Group ，便于调整相对层级关系

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• Combine elements' container

In the previous logic, nodes, edges, and combinations were placed in three groups respectively, resulting in the element hierarchy always being fixed as: Nodes > Edges > Combinations
Now all elements are placed in the same Group, which is easy to adjust the relative hierarchy relationship

relative issue: #5836 #5821