Create a script for generating bignum tests

[gilles-peskine-arm]

Create a script for generating unit tests in a systematic way. This is similar to tests/scripts/generate_psa_tests.py.

To start with, generate a few bignum simple test cases (into a new file test_suite_bignum.generated.data) for one or more existing test function, just to get the framework started. There will be follow-ups to generate useful bignum and crypto test cases.

Make sure that the new test data file is taken into account wherever they need to be. New data files will be added later, so call tests/scripts/generate_bignum_tests.py --list, don't hard-code the list of generated files if not absolutely necessary. Check where generate_psa_tests.py is called; generate_bignum_tests.py will likely need to be called in the same places. In particular, both with make (**/Makefile) and with CMake (**/CMakeLists.txt):

• Building the unit test must build the new test suite.
• Running the unit tests must run the new test suite.
• make generated_files must generate the new data file.
• tests/scripts/check_generated_files.sh must take the new generated file into account.
• In 2.28, the new file must be checked into git. In development, it must be .gitignored.