Asymmetric key data unit tests

[gilles-peskine-arm]

Validate asymmetric key data. Uses the OpenSSL 3 command line, because that turned out to be convenient.

This will avoid a repeat of https://github.com/Mbed-TLS/mbedtls/pull/8986#discussion_r1562655123, and make reviewing future changes to asymmetric_key_data.py easier.

Needs https://github.com/Mbed-TLS/mbedtls/pull/9101 because I want to use subprocess.check_output and this requires upgrading pylint and mypy to slightly less old versions.

PR checklist

• [x] changelog no (test only)
• [ ] 3.6 backport TODO
• [x] 2.28 backport no need: at this point, any relevant test data added to 2.28 is very likely to be backported from development where it will have been validated.
• [x] tests provided