Enable within Expression with layout property

[zmiao]

This pr implement usage of within expression with layout property. Currently the usage is: [within, geoJSONObj]. It returns true if the feature is inside the geometry boundary that defined by geoJSONObj. geoJSONObj should be inlined.

Following example shows how to set different text contents based on the feature's geometry location.

{
        "id": "text",
        "type": "symbol",
        "source": "points",
        "layout": {
            "text-field": ["case", ["within", {
                "type": "Polygon",
                "coordinates": [
                    [
                      [0, 0],
                      [0, 5],
                      [5, 5],
                      [5, 0],
                      [0, 0]
                    ]
                  ]
                }], "In", "Out"],
            "text-font": [
                "Open Sans Semibold",
                "Arial Unicode MS Bold"
            ],
            "text-size": 10
          },
          "paint" : {
            "text-color": "red"
          }
 }

[alexshalamov]

lgtm, +changelog