[ Merge of http://go/wvgerrit/115545 ]
This change wraps the RSA key in a public and private key class that is
similar to how ECC keys are wrapped.
This new wrapper replaces deprecated OpenSSL/BoringSSL RSA signing and
signature verification API and uses the generic key digest context for
RSASSA-PSS signatures.
Bug: 135283522
Test: Future CL
Change-Id: Ifff649a3abcca127cc539f937c429c7da8acdcc6
7a46bc3c87