add expected_rent_collection (#24028)

* add expected_rent_collection

* update some comments for clarity and resolve a todo

* add test for 'LeaveAloneNoRent'

runtime/src/lib.rs

@@ -30,6 +30,7 @@ pub mod cost_model;
 pub mod cost_tracker;
 pub mod epoch_stakes;
 pub mod execute_cost_table;
+mod expected_rent_collection;
 pub mod genesis_utils;
 pub mod hardened_unpack;
 pub mod in_mem_accounts_index;