Add support for iOS attestation

Renamed verifyDeviceAttestation to verifyAndroidAttestation and added a new verifyIosAttestation function. The AttestAndSign handler now uses a switch statement based on service type to call either verifyIosAttestation or verifyAndroidAttestation when the EnablePiInIos experiment is enabled.

PiperOrigin-RevId: 892545054

quiche/blind_sign_auth/proto/attestation.proto

diff --git a/quiche/blind_sign_auth/proto/attestation.proto b/quiche/blind_sign_auth/proto/attestation.proto
index 3ad7108..31e31ea 100644
--- a/quiche/blind_sign_auth/proto/attestation.proto
+++ b/quiche/blind_sign_auth/proto/attestation.proto
@@ -105,6 +105,12 @@
   // AppAttest attestation token.
   // Encoded in CBOR format.
   bytes attestation_token = 1;
+
+  // AppAttest vendor ID.
+  string ios_vendor_id = 2;
+
+  // Device ID for quota checking.
+  string device_id = 3;
 }
 
 message AttestationData {