Set up a code generation framework for driver wrappers

[gilles-peskine-arm]

The unified driver interface framework in #3313 is designed to be implemented with generated code to call the drivers.

We need a framework to generate this wrapper code for Mbed TLS. The generation code will be in Python 3 since this is our scripting language. This is an investigation task; the outcome is not precisely defined, but will likely be Python code that can handle at least one smoke-test driver, as well as guidelines for the interface (types and function prototypes) between the hand-written code and the generated code.

#3313 has some ad hoc string writing code. This may or may not be the correct answer.

3rd March 2021: We have an hand-made driver wrapper to test the driver delegations we support. For multi-part operations (only multi-part cipher operations supported as time of writing but more to come soon), the driver operation context is dynamically allocated. This should be revisited to avoid dynamic allocations (see #4157 (comment)).

[gilles-peskine-arm]

Fulfilled by #5193 and its follow-ups.