PROV: Implement padding mode words in the RSA ASYM_CIPHER implementation

PROV: Implement padding mode words in the RSA ASYM_CIPHER implementation

Because the libcrypto code has relinquished control of exact words to
express padding mode choices, we re-implement them in the appropriate
provider implementation.

For the sake of legacy controls, we maintain support for the numeric
form of the padding mode, but leave that support otherwise undeclared.

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/10947)