Use explicit values for HandshakeProtocol

So that we can implement comparators and/or hashers.

PiperOrigin-RevId: 777336057

quiche/quic/core/quic_versions.h

diff --git a/quiche/quic/core/quic_versions.h b/quiche/quic/core/quic_versions.h
index f8fe6ed..18bf1f9 100644
--- a/quiche/quic/core/quic_versions.h
+++ b/quiche/quic/core/quic_versions.h
@@ -148,9 +148,9 @@
 // We are planning on eventually deprecating PROTOCOL_QUIC_CRYPTO in favor of
 // PROTOCOL_TLS1_3.
 enum HandshakeProtocol {
-  PROTOCOL_UNSUPPORTED,
-  PROTOCOL_QUIC_CRYPTO,
-  PROTOCOL_TLS1_3,
+  PROTOCOL_UNSUPPORTED = 0,
+  PROTOCOL_QUIC_CRYPTO = 1,
+  PROTOCOL_TLS1_3 = 2,
 };
 
 // Helper function which translates from a HandshakeProtocol to a string.