Use `rsaEncryption` OID during exporting for all RSA algorithms

[lucacasonato]

Somewhat unrelated; while testing, I noticed that when exporting, all implementations I tested set the OID to rsaEncryption for both algorithms, rather than id-RSASSA-PSS and id-RSAES-OAEP respectively. Even though I think that's not ideal, maybe we should change the spec to match that as well, given such broad consensus.

Originally posted by @twiss in #297 (comment)

[panva]

this is also the case for id-ecDH, only ecPublicKey is being used instead.