Add support for parsing MLT-format vector tile sources (#3246)

Co-authored-by: Bart Louwers <bart@emeel.net>
Co-authored-by: Bart Louwers <bart.louwers@gmail.com>

test/tile/tile_cache.test.cpp

@@ -5,7 +5,7 @@
 #include <mbgl/test/fake_file_source.hpp>
 #include <mbgl/tile/tile_loader_impl.hpp>
 #include <mbgl/tile/vector_tile.hpp>
-#include <mbgl/tile/vector_tile_data.hpp>
+#include <mbgl/tile/vector_mvt_tile_data.hpp>
 
 #include <mbgl/actor/scheduler.hpp>
 #include <mbgl/annotation/annotation_manager.hpp>
@@ -38,6 +38,8 @@ public:
         renderable = true;
     }
 
+    void setData(const std::shared_ptr<const std::string>&) override {}
+
     util::SimpleIdentity uniqueId;
 };