[core] Added mbgl::util::convert helper function

Converts a given std::array into another using a different (convertible)
type.

include/mbgl/util/convert.hpp

@@ -0,0 +1,17 @@
+#include <array>
+#include <type_traits>
+#include <utility>
+
+namespace mbgl {
+namespace util {
+
+template<typename To, typename From, std::size_t Size,
+         typename = std::enable_if_t<std::is_convertible<From, To>::value>>
+constexpr std::array<To, Size> convert(const std::array<From, Size>&from) {
+    std::array<To, Size> to {};
+    std::copy(std::begin(from), std::end(from), std::begin(to));
+    return to;
+}
+
+} // namespace util
+} // namespace mbgl

src/mbgl/util/convert.cpp

@@ -0,0 +1,9 @@
+#include <mbgl/util/convert.hpp>
+
+namespace mbgl {
+namespace util {
+
+template std::array<float, 2> convert(const std::array<int32_t, 2>&);
+
+} // namespace util
+} // namespace mbgl