Slimmer implementation of credit-only accounts (#4592)

* Add credit-only debit/data check to verify_instruction

* Store credits and pass to accounts_db

* Add InstructionErrors and tests

* Relax account locks for credit-only accounts

* Collect credit-only account credits before passing to accounts_db to store properly

* Convert System Transfer  accounts to credit-only, and fixup test

* Functionalize collect_accounts to unit test

* Review comments

* Rebase

sdk/src/account.rs

@@ -55,6 +55,8 @@ impl Account {
     }
 }
 
+pub type LamportCredit = u64;
+
 #[repr(C)]
 #[derive(Debug)]
 pub struct KeyedAccount<'a> {