- Implicitly fixes invoke_context.return_data not being reset between instructions in process_message. (#21671) (#21684)

- Lets InvokeContext::process_cross_program_instruction() handle the first invocation depth too.
- Marks InvokeContext::verify(), InvokeContext::verify_and_update() and InvokeContext::process_executable_chain() private.
- Renames InvokeContext::process_cross_program_instruction() to InvokeContext::process_instruction().
- Removes InvokeContext::new_mock_with_sysvars().

(cherry picked from commit 1df88837c8)

Co-authored-by: Alexander Meißner <AlexanderMeissner@gmx.net>

program-test/src/lib.rs

@@ -319,8 +319,9 @@ impl solana_sdk::program_stubs::SyscallStubs for SyscallStubs {
         }
 
         invoke_context
-            .process_cross_program_instruction(
+            .process_instruction(
                 &message,
+                &message.instructions[0],
                 &program_indices,
                 &account_indices,
                 &caller_privileges,