Rename internal operation definitions

Context

Closes #2806 (closed).

The following definitions are renamed (along with related constructors and functions), hopefully for better clarity and consistency:

• Script_typed_ir.manager_operation to internal_operation_contents;
• (Script_typed_ir.packed_manager_operation is removed because it is unused;)
• Apply_internal_results.internal_manager_operation to internal_operation_contents;
• Apply_internal_results.packed_internal_manager_operation to packed_internal_operation_contents;
• Apply_internal_results.internal_contents to internal_operation;
• Apply_internal_results.packed_internal_contents to packed_internal_operation;
• Apply_internal_results.successful_internal_manager_operation_result to successful_internal_operation_result;
• Apply_internal_results.packed_successful_internal_manager_operation_result to packed_successful_internal_operation_result;
• Apply_internal_results.internal_manager_operation_result to internal_operation_result;
• Apply_internal_results.packed_internal_manager_operation_result to packed_internal_operation_result;
• Apply_internal_results.Internal_result to Internal_operation;
• Apply_internal_results.Internal_manager_result to Internal_operation_result;
• Apply.apply_manager_operation to apply_manager_operations;
• Apply.apply_external_manager_operation_content to apply_manager_operation.

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