ABI: Support sequencing bare app call and method invocations

## Problem

As of writing, PyTeal doesn't support the following clause from https://github.com/algorandfoundation/ARCs/blob/main/ARCs/arc-0004.md#oncompletion-actions-and-creation:

> If a Contract elects to allow bare Application calls for some OnCompletion actions, then that Contract SHOULD also allow any of its methods to be called with those OnCompletion actions, as long as this would not cause undesirable or nonsensical behavior.

The story's request is to provide a configuration mechanism enabling app developers to choose desired behavior.
* For each OnCompletion action, the developer can opt-in for invoking associated bare app call handler + method handler.
* Backwards compatibility concern: If there's a desire to change default Router behavior from _not_ sequencing to sequencing, we must either:
* Implement a Router-level (or similar) versioning and/or feature flag scheme enabling developers to upgrade pyteal _without_ changing generated TEAL.
* Reach team agreement that a minor or major pyteal version bump is sufficient notice for behavior change.

## Solution

## Dependencies

## Urgency