Keystore: Support Curve 25519 in the SPI layer

Add support for Curve 25519 in the public API.
This requires upgrading the keymint dependency to V2.

Note that this CL only passes tha tags to Keystore,
but does not yet let the caller use the generated keys
because of missing Conscrypt classes.

Bug: 194359292
Test: atest android.keystore.cts.Curve25519Test
Change-Id: I15223abec34b72c857e26fcc47d8ecf08c1f8c8d