Keystore 2.0 SPI: Duplicate Keystore SPI to android.security.keystore2 package

This patch copies the relevant portion of the Keystore SPI to the new
package name android.security.keystore2. The purpose of this is to
illustrate the evolution from the existing Keystore SPI to the
Keystore 2.0 SPI while keeping the existing Keystore SPI intact.
Reviewers are advised to check the equivalence of this code to the
corresponding files in
    android/security/keystore (<-- no 2 here).
Subsequent patches can them be reviewed as evolution towards the new SPI
rather than completely new code.

Test: None. When the evolution is complete, Keystore CTS tests can be
used to check for regressions.
Bug: 159476414

Change-Id: I21a01a679e789868ce820b5f73221e616a456a61