Accept constant expressions in non-dds properties (#11961)

Closes #11940

test/style/conversion/property_value.test.cpp

@@ -0,0 +1,21 @@
+#include <mbgl/test/util.hpp>
+
+#include <mbgl/style/conversion/json.hpp>
+#include <mbgl/style/conversion/property_value.hpp>
+#include <mbgl/util/rapidjson.hpp>
+
+using namespace mbgl;
+using namespace mbgl::style;
+using namespace mbgl::style::conversion;
+
+TEST(StyleConversion, PropertyValue) {
+    // PropertyValue<T> accepts a constant expression: https://github.com/mapbox/mapbox-gl-native/issues/11940
+    Error error;
+    JSDocument doc;
+    doc.Parse<0>(R"(["literal", [1, 2]])");
+    auto expected = std::array<float, 2>{{1, 2}};
+    auto result = convert<PropertyValue<std::array<float, 2>>>(doc, error);
+    ASSERT_TRUE(result);
+    ASSERT_TRUE(result->isConstant());
+    ASSERT_EQ(result->asConstant(), expected);
+}