[build] Make the default styles part of GL Native

The reason is applications using it, like GLFW, don't need
to depend on code inside platform/default.

include/mbgl/util/default_styles.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <vector>
+#include <string>
+
+namespace mbgl {
+namespace util {
+namespace default_styles {
+
+struct DefaultStyle {
+    const char* url;
+    const char* name;
+    const unsigned currentVersion;
+};
+
+constexpr const DefaultStyle streets          = { "mapbox://styles/mapbox/streets-v11",           "Streets",           11 };
+constexpr const DefaultStyle outdoors         = { "mapbox://styles/mapbox/outdoors-v11",          "Outdoors",          11 };
+constexpr const DefaultStyle light            = { "mapbox://styles/mapbox/light-v10",             "Light",             10 };
+constexpr const DefaultStyle dark             = { "mapbox://styles/mapbox/dark-v10",              "Dark",              10 };
+constexpr const DefaultStyle satellite        = { "mapbox://styles/mapbox/satellite-v9",          "Satellite",          9 };
+constexpr const DefaultStyle satelliteStreets = { "mapbox://styles/mapbox/satellite-streets-v11", "Satellite Streets", 11 };
+
+const DefaultStyle orderedStyles[] = {
+    streets, outdoors, light, dark, satellite, satelliteStreets,
+};
+const size_t numOrderedStyles = sizeof(orderedStyles) / sizeof(DefaultStyle);
+
+} // end namespace default_styles
+} // end namespace util
+} // end namespace mbgl