17066: sys/irq: Add C++ wrapper using RAII r=maribu a=jenswet
### Contribution description
This adds a C++ wrapper around the `irq.h` API. The wrapper uses RAII to accomplish a convenient and bug resistent use.
A little background: I'm currently writing my master thesis on using C++ for embedded development, at the working group that `@maribu` is part of. For that I will try to add better C++ support to several parts of RIOT and then do some benchmarking and metrics to compare it with the C implementation. For example, I also plan to add a wrapper around i2c, a std::cout drop-in replacement and probably some more about networks or threads.
### Testing procedure
I've added a unit test to verify that the IRQ wrapper calls the original `irq` functions as expected. As C++ and wrapper testing isn't done much so far in this project, I've added two additional headers to ease testing:
1. #17076 - fake functions framework, already merged
2. As there is no framework for C++ unit tests yet, I've added something for this too. Unfortunately the existing frameworks like GoogleTest, CppUTest or CppUnit don't easily compile for embedded or are difficult to integrate in to the RIOT build process. That's why I wrote some (simple) helper functions and macros inspired by the above frameworks. That allows to create C++ tests based on a fixture class with set up and tear down methods. It also allows some simple assertions and is easily extendable for other use cases. It wraps some of the fff functionality too.
Both of this is obviously not required for the initial reason of this PR. But I'd like to provide unit tests for the features that I suggest to introduce where possible. So I'd appreciate some feedback on that too. If you'd prefer a PR without or different tests please let me know.
You can run the test `irq_cpp` locally or on the CI to test the implementation.
Please feel free to give feedback or suggest improvements!
Co-authored-by: Jens Wetterich <jens@wetterich-net.de>
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