Bad sizing when running layoutEditorGroups twice

[aeschli]

Testing #50458

• add a new keybinding

    {
        "key": "Ctrl+0",
        "command": "layoutEditorGroups",
        "args": {
            "orientation": 1,
            "groups": [{ "size": 0.2 }, { "size": 0.2 }, { "size": 0.6, "groups": [{}, {}] }]
        }
    }

• invoke the keybinding: new empty groups are added with the sizes as specified
• invoke the keybinding again: the groups are resized, not following the sizes as specified

[bpasero]

Adding @joaomoreno, as discussed this would need a bit of support from the grid widget to deserialize a set of groups with certain layout.