Add raw RSA signature support

With the new Keystore changes, this is the only way you can get raw RSA
signatures which a lot of native code expects to be able to do.

(cherry-picked from c531f5f402b4cedcc35a0b7f0b540dc84c545106)

Bug: 6787078
Change-Id: I1c5ddd5287be1ab71347eedc864a41c24e156cb4
5 files changed