Use StringBuilder for GetString/GetStringWithArgs, as per upstream

Update dependent code as required

src/town_cmd.cpp

@@ -252,9 +252,7 @@ uint64 Town::LabelParam2() const
 
 void Town::FillCachedName() const
 {
-	char buf[MAX_LENGTH_TOWN_NAME_CHARS * MAX_CHAR_LENGTH];
-	char *end = GetTownName(buf, this, lastof(buf));
-	this->cached_name.assign(buf, end);
+	this->cached_name = GetTownName(this);
 }
 
 /**