The import key operations of
- RSASSA-PKCS1-v1_5 (`rsassa_pkcs1_v1_5_operation::import_key`)
- RSA-PSS (`rsa_pss::import_key`)
- RSA_OAEP (`rsa_oaep::import_key`)
only differ from each other by a few steps. This patch combines them
into a single function (`rsa_common::import_key`) shared among them.
The enum variant `RsaAlgorithm::RsaSsaPkcs1v15` is also renamed as
`RsaAlgorithm::RsassaPkcs1v1_5` for clarity.
Testing: Refactoring. Existing tests suffice.
Signed-off-by: Kingsley Yung <kingsley@kkoyung.dev>