Added release function to PoolVector::Access.

For clarity, assign-to-release idiom for PoolVector::Read/Write
replaced with a function call.
Existing uses replaced (or removed if already handled by scope)

scene/2d/tile_map.cpp

@@ -1275,7 +1275,7 @@ PoolVector<int> TileMap::_get_tile_data() const {
 		idx += 3;
 	}
 
-	w = PoolVector<int>::Write();
+	w.release();
 
 	return data;
 }