Add render test to verify that linear filtering is used

Test that linear filtering is used for icons in text when
text-size is zoom-dependent.

test/integration/render-tests/text-field/formatted-images-zoom-dependent-size/style.json

@@ -0,0 +1,69 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "height": 128,
+      "width": 128,
+      "allowed": 0.014
+    }
+  },
+  "center": [ 0, 0 ],
+  "zoom": 12,
+  "sources": {
+    "point": {
+      "type": "geojson",
+      "data": {
+        "type": "FeatureCollection",
+        "features": [
+          {
+            "type": "Feature",
+            "geometry": {
+              "type": "Point",
+              "coordinates": [ 0, 0 ]
+            }
+          }
+        ]
+      }
+    }
+  },
+  "glyphs": "local://glyphs/{fontstack}/{range}.pbf",
+  "sprite": "local://sprites/emerald@2x",
+  "layers": [
+    {
+      "id": "text_zoom_constant",
+      "type": "symbol",
+      "source": "point",
+      "layout": {
+        "text-offset": [0, -1],
+        "text-size": [
+          "interpolate",
+          ["linear"],
+          ["zoom"],
+          4,
+          8,
+          20,
+          34
+        ],
+        "text-field": ["format", "Zoom", ["image", "rer"]],
+        "text-font": [
+          "Open Sans Semibold",
+          "Arial Unicode MS Bold"
+        ]
+      }
+    },
+    {
+      "id": "text_zoom_dependent",
+      "type": "symbol",
+      "source": "point",
+      "layout": {
+        "text-offset": [0, 1],
+        "text-size": 21,
+        "text-field": ["format", "Zoom", ["image", "rer"]],
+        "text-font": [
+          "Open Sans Semibold",
+          "Arial Unicode MS Bold"
+        ]
+      }
+    }
+  ]
+}