MINOR: quic: support hq-interop

Implement a new app_ops layer for quic interop. This layer uses HTTP/0.9
on top of QUIC. Implementation is minimal, with the intent to be able to
pass interoperability test suite from
https://github.com/marten-seemann/quic-interop-runner.

It is instantiated if the negotiated ALPN is "hq-interop".
diff --git a/Makefile b/Makefile
index f5dfed2..c7d6ee9 100644
--- a/Makefile
+++ b/Makefile
@@ -594,7 +594,8 @@
 ifneq ($(USE_QUIC),)
 OPTIONS_OBJS += src/quic_sock.o src/proto_quic.o src/xprt_quic.o src/quic_tls.o \
                 src/quic_frame.o src/quic_cc.o src/quic_cc_newreno.o src/mux_quic.o \
-                src/cbuf.o src/qpack-dec.o src/qpack-tbl.o src/h3.o src/qpack-enc.o
+                src/cbuf.o src/qpack-dec.o src/qpack-tbl.o src/h3.o src/qpack-enc.o \
+                src/hq_interop.o
 endif
 
 ifneq ($(USE_LUA),)