fix: do not ovelap hoverlabels for different tracetypes

[mbant]

This PR attempts a fix for #6917 which reported excessive hoverlabel removal and overlap for plots with both scatter and bar traces.

Behaviour before the fix:

or even

Behaviour after the fix:

JSON file used for the example

{
  "data": [
    {
      "name": "scatter_1",
      "type": "scatter",
      "y": [0, 1, 2],
      "x": ["CAT 1", "CAT 2", "CAT 3"]
    },
    {
      "name": "bar_1",
      "type": "bar",
      "y": [0, 1, 2],
      "x": ["CAT 1", "CAT 2", "CAT 3"]
    },
    {
      "name": "scatter_2",
      "type": "scatter",
      "x": ["CAT 1", "CAT 2", "CAT 3"],
      "y": [0, 1, 2]
    },
    {
      "name": "bar_2",
      "type": "bar",
      "y": [0, 1, 2],
      "x": ["CAT 1", "CAT 2", "CAT 3"]
    },
    {
      "name": "scatter_3",
      "type": "scatter",
      "x": ["CAT 1", "CAT 2", "CAT 3"],
      "y": [0, 1, 2]
    },
    {
      "name": "bar_3",
      "type": "bar",
      "y": [0, 1, 2],
      "x": ["CAT 1", "CAT 2", "CAT 3"]
    }
  ],
  "layout": {
    "width": 600,
    "height": 400,
    "hovermode": "x"
  }
}