feat(dataviz): redo region selection

[hydrosquall]

PR Description

• Clean slate approach to feat: Region Selections Vega-Lite #9536

Changes

Testing

• Try visiting this spec

{
  "$schema": "https://vega.github.io/schema/vega-lite/v6.json",
  "data": {
    "url": "https://vega.github.io/vega-lite/data/cars.json"
  },
  "params": [
    {
      "name": "brush",
      "select": "region"
    }
  ],
  "mark": "point",
  "encoding": {
    "x": {
      "field": "Horsepower",
      "type": "quantitative"
    },
    "y": {
      "field": "Miles_per_Gallon",
      "type": "quantitative"
    },
    "color": {
      "condition": {
        "param": "brush",
        "field": "Cylinders",
        "type": "ordinal"
      },
      "value": "grey"
    }
  }
}

[cloudflare-workers-and-pages]

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