[core] Avoid public dtoa.hpp include

src/mbgl/util/string.cpp

@@ -0,0 +1,20 @@
+#include <mbgl/util/string.hpp>
+#include <mbgl/util/dtoa.hpp>
+
+namespace mbgl {
+namespace util {
+
+std::string toString(float num) {
+    return dtoa(num);
+}
+
+std::string toString(double num) {
+    return dtoa(num);
+}
+
+std::string toString(long double num) {
+    return dtoa(num);
+}
+
+} // namespace util
+} // namespace mbgl