[core] reparse tiles when new data arrives

We're now reparsing tiles when they expire. We're also swapping out buckets atomically to avoid flickering data; i.e. we're displaying the old data as long as we don't have a new parsed bucket for that layer yet. The parsed buckets now live in the *TileData objects rather than in the TileWorker; only partially parsed == pending buckets will remain in the TileWorker. Once they're parsed, they're moved to the *TileData object.

src/mbgl/map/tile_data.cpp

@@ -1,11 +1,26 @@
 #include <mbgl/map/tile_data.hpp>
+#include <mbgl/renderer/debug_bucket.hpp>
 
-using namespace mbgl;
+namespace mbgl {
 
 TileData::TileData(const TileID& id_)
     : id(id_),
-      debugBucket(debugFontBuffer),
       state(State::initial) {
-    // Initialize tile debug coordinates
-    debugFontBuffer.addText(std::string(id).c_str(), 50, 200, 5);
 }
+
+TileData::~TileData() = default;
+
+const char* TileData::StateToString(const State state) {
+    switch (state) {
+        case TileData::State::initial: return "initial";
+        case TileData::State::invalid : return "invalid";
+        case TileData::State::loading : return "loading";
+        case TileData::State::loaded : return "loaded";
+        case TileData::State::obsolete : return "obsolete";
+        case TileData::State::parsed : return "parsed";
+        case TileData::State::partial : return "partial";
+        default: return "<unknown>";
+    }
+}
+
+} // namespace mbgl