Move API-only header files out of core/io into core

Since those do not rely on any I/O functions, and are used by other parts of QUICHE that do not rely on I/O functions (e.g. QuicSimpleServerBackend), those shouldn't be in core/io.

PiperOrigin-RevId: 475374083
diff --git a/quiche/quic/tools/quic_server.h b/quiche/quic/tools/quic_server.h
index cf71ac6..f97a459 100644
--- a/quiche/quic/tools/quic_server.h
+++ b/quiche/quic/tools/quic_server.h
@@ -17,11 +17,11 @@
 #include "quiche/quic/core/crypto/quic_crypto_server_config.h"
 #include "quiche/quic/core/deterministic_connection_id_generator.h"
 #include "quiche/quic/core/io/quic_event_loop.h"
-#include "quiche/quic/core/io/socket_factory.h"
 #include "quiche/quic/core/quic_config.h"
 #include "quiche/quic/core/quic_packet_writer.h"
 #include "quiche/quic/core/quic_udp_socket.h"
 #include "quiche/quic/core/quic_version_manager.h"
+#include "quiche/quic/core/socket_factory.h"
 #include "quiche/quic/platform/api/quic_socket_address.h"
 #include "quiche/quic/tools/quic_simple_server_backend.h"
 #include "quiche/quic/tools/quic_spdy_server_base.h"