Add CPI support for upgradeable loader (#14193)

sdk/src/process_instruction.rs

@@ -61,6 +61,8 @@ pub trait InvokeContext {
     fn record_instruction(&self, instruction: &Instruction);
     /// Get the bank's active feature set
     fn is_feature_active(&self, feature_id: &Pubkey) -> bool;
+    /// Get an account from a pre-account
+    fn get_account(&self, pubkey: &Pubkey) -> Option<Account>;
 }
 
 #[derive(Clone, Copy, Debug, AbiExample)]
@@ -340,4 +342,7 @@ impl InvokeContext for MockInvokeContext {
     fn is_feature_active(&self, _feature_id: &Pubkey) -> bool {
         true
     }
+    fn get_account(&self, _pubkey: &Pubkey) -> Option<Account> {
+        None
+    }
 }