Missing ASN1 functions in a build with RSA_C

[valeriosetti]

Summary

RSA module depends on ASN1 functions for parsing and writing public and private keys. However:

• there is no check that MBEDTLS_ASN1_[WRITE|PARSE]_C are enabled in check_config.h, or
• MBEDTLS_ASN1_[WRITE|PARSE]_C are not automatically-enabled when MBEDTLS_RSA_C is enabled.

The result is that a build where RSA is enabled while ASN1 is disabled will not build at all due to missing symbols at link time.

The goal of this issue is to implement one of the two options above (preferably the 2nd one since it's more backward compatible).

System information

Mbed TLS version (number or commit id): 3.6.0
Operating system and version: not relevant
Configuration (if not default, please attach mbedtls_config.h): default without ASN1 (and connected dependencies on check_config.h such as ECDSA and PK)
Compiler and options (if you used a pre-built binary, please indicate how you obtained it): n/a
Additional environment information: n/a