[core] Fix misc-* errors

As reported by clang-tidy-8.

platform/default/src/mbgl/storage/sqlite3.cpp

@@ -132,7 +132,7 @@ mapbox::util::variant<Database, Exception> Database::tryOpen(const std::string &
 Database Database::open(const std::string &filename, int flags) {
     auto result = tryOpen(filename, flags);
     if (result.is<Exception>()) {
-        throw result.get<Exception>();
+        throw std::move(result.get<Exception>());
     } else {
         return std::move(result.get<Database>());
     }

platform/node/src/node_map.cpp

@@ -315,7 +315,7 @@ NodeMap::RenderOptions NodeMap::ParseOptions(v8::Local<v8::Object> obj) {
         if (auto light = mbgl::style::conversion::convert<mbgl::style::Light>(lightObj, conversionError)) {
             options.light = *light;
         } else {
-            throw conversionError;
+            throw std::move(conversionError);
         }
     }
 

src/mbgl/annotation/shape_annotation_impl.cpp

@@ -11,7 +11,6 @@
 namespace mbgl {
 
 using namespace style;
-namespace geojsonvt = mapbox::geojsonvt;
 
 ShapeAnnotationImpl::ShapeAnnotationImpl(const AnnotationID id_)
     : id(id_),

src/mbgl/renderer/render_orchestrator.cpp

@@ -43,16 +43,16 @@ public:
     LayerRenderItem(RenderLayer& layer_, RenderSource* source_, uint32_t index_)
         : layer(layer_), source(source_), index(index_) {}
     bool operator<(const LayerRenderItem& other) const { return index < other.index; }
+
     std::reference_wrapper<RenderLayer> layer;
     RenderSource* source;
+    const uint32_t index;
 
 private:
     bool hasRenderPass(RenderPass pass) const override { return layer.get().hasRenderPass(pass); }
     void upload(gfx::UploadPass& pass) const override { layer.get().upload(pass); }
     void render(PaintParameters& parameters) const override { layer.get().render(parameters); }
     const std::string& getName() const override { return layer.get().getID(); } 
-
-    uint32_t index;
 };
 
 class RenderTreeImpl final : public RenderTree {