feat(editor): map browser for loading existing WoW zones

- Load Map Tile dialog now shows a searchable list of all available
  maps from the manifest (Azeroth, Kalimdor, Outland, dungeons, etc.)
- Click a map name to select it, then pick tile X/Y coordinates
- Helpful tile range hints shown below coordinates
- Maps indexed from WDT files in the manifest on startup
- Foundation for loading and modifying sections of existing WoW maps

tools/editor/asset_browser.hpp

@@ -27,6 +27,8 @@ public:
     const std::vector<std::string>& getM2Directories() const { return m2Dirs_; }
     const std::vector<std::string>& getWMODirectories() const { return wmoDirs_; }
 
+    const std::vector<std::string>& getMapNames() const { return mapNames_; }
+
     bool isInitialized() const { return initialized_; }
 
 private:
@@ -39,6 +41,7 @@ private:
     std::vector<std::string> textureDirs_;
     std::vector<std::string> m2Dirs_;
     std::vector<std::string> wmoDirs_;
+    std::vector<std::string> mapNames_;
     bool initialized_ = false;
 };