Params cannot be common to individual Layers.

[VikrantRamesh]

Bug Description

I encountered a bug where I cannot place params common to all the layers and modify the opacity with respect to them.
(Open the Chart in the Vega Editor) . Please do let me know if there is a work-around. Find the json below:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"url": "data/seattle-weather.csv"},
  "width": 500,
  "transform": [
    {
      "calculate": "random() < 0.5 ? 'north' : 'south'",
      "as": "region"
    }
  ],
  "params": [
    {
      "name": "legendSelection",
      "select": {"type": "point", "fields": ["combinedColumn"]},
      "bind": "legend"
    }
  ],
  "layer": [
    {
      // Tab 1
      "layer": [
        {
          "layer": [
            {
              "mark": {"type": "bar"},
              "encoding": {
                "x": {
                  "timeUnit": "month",
                  "field": "date",
                  "type": "ordinal"
                },
                "y": {
                  "aggregate": "sum",
                  "field": "temp_min",
                  "type": "quantitative"
                },
                "color": {"datum": "temp_min"},
                "opacity": {
                  "condition": {
                    "param": "legendSelection",
                    "value": 1
                  },
                  "value": 0.3
                }
              }
            }
          ]
        }
      ]
    },
    {
      // Tab 2
      "layer": [
        {
          "transform": [
            {
              "fold": ["precipitation", "temp_max"],
              "as": ["metric", "value"]
            },
            {
              "calculate": "datum.weather + ' - ' + datum.metric",
              "as": "combinedColumn"
            }
          ],
          "encoding": {
            "color": {"field": "combinedColumn", "type": "nominal"}
          },
          "layer": [
            {
              "transform": [{"filter": "datum.metric == 'precipitation'"}],
              "mark": {
                "type": "line",
                "interpolate": "linear",
                "point": {"fill": "white", "filled": false},
                "strokeDash": [1, 0],
                "tooltip": true
              },
              "encoding": {
                "x": {
                  "timeUnit": "month",
                  "field": "date",
                  "type": "ordinal"
                },
                "y": {
                  "aggregate": "sum",
                  "field": "precipitation",
                  "type": "quantitative"
                },
                "opacity": {
                  "condition": {
                    "param": "legendSelection",
                    "value": 1
                  },
                  "value": 0.3
                }
              }
            },
            {
              "transform": [{"filter": "datum.metric == 'temp_max'"}],
              "mark": {
                "type": "line",
                "interpolate": "linear",
                "point": {"fill": "white", "filled": false},
                "strokeDash": [1, 0],
                "tooltip": true
              },
              "encoding": {
                "x": {
                  "timeUnit": "month",
                  "field": "date",
                  "type": "ordinal"
                },
                "y": {
                  "aggregate": "sum",
                  "field": "temp_max",
                  "type": "quantitative"
                },
                "opacity": {
                  "condition": {
                    "param": "legendSelection",
                    "value": 1
                  },
                  "value": 0.3
                }
              }
            }
          ]
        }
      ]
    }
  ]
}

It throws the following Error:

Duplicate signal name: "legendSelection_tuple"