if there is extension_list, then the builtin_list would be replaced/overriden. e.g. if there are 3 items in extension_list, then first 3 items in builtin_list would be replaced when you type `:Telescope fi` and press tab to get completion list.
if there is extension_list, then the builtin_list would be replaced/overriden. e.g. if there are 3 items in extension_list, then first 3 items in builtin_list would be replaced when you type `:Telescope fi` and press tab to get completion list.