KeyStore: X25519 key import

Added a KeyAgreement algorithm for X25519(XDH) in KeyProperties.
KM_ALGORITHM_EC is used for XDH because Keymint uses KM_ALGORITHM_EC along
with Curve25519 to differentiate X25519 and other EC keys.

Algorithm name XDH is set for X25519 private key.

Consilidated methods of Keymaster specific conversions of EC_CURVE into
KeymasterUtil.

Bug: 240682299
Test: run cts -m CtsKeystoreTestCases -t android.keystore.cts.Curve25519Test#x25519KeyImportAndAgreementTest
Change-Id: I3f95738194e62be0f1d821b1eb467ed810a5a175