Implement interruptible ECC Export Public Key (Complete / Tests)

[paul-elliott-arm]

Stage 3 of implementing interruptible ECC export public key.

This should involve implementing psa_export_public_key_iop_complete() and include any testing that we can do of this function to ensure it is functionally correct. This should also include full testing of the iop export public key sequence (start / complete / abort) including testing of calling out of order and other negative tests.

Remember that abort should be called internally in case of any error.

Function prototype for reference:

psa_status_t psa_export_public_key_iop_complete(psa_export_public_key_iop_t * operation,
                                                uint8_t * data,
                                                size_t data_size,
                                                size_t * data_length);