Initial HTTP/3 implementation

This includes Websocket over HTTP/3.

Since quicer, which provides the QUIC implementation,
is a NIF, Cowboy cannot depend directly on it. In order
to enable QUIC and HTTP/3, users have to set the
COWBOY_QUICER environment variable:

  export COWBOY_QUICER=1

In order to run the test suites, the same must be done
for Gun:

  export GUN_QUICER=1

HTTP/3 support is currently not available on Windows
due to compilation issues of quicer which have yet to
be looked at or resolved.

HTTP/3 support is also unavailable on the upcoming
OTP-27 due to compilation errors in quicer dependencies.
Once resolved HTTP/3 should work on OTP-27.

Because of how QUIC currently works, it's possible
that streams that get reset after sending a response
do not receive that response. The test suite was
modified to accomodate for that. A future extension
to QUIC will allow us to gracefully reset streams.

This also updates Erlang.mk.

test/tracer_SUITE.erl

@@ -29,7 +29,8 @@ suite() ->
 %% We initialize trace patterns here. Appropriate would be in
 %% init_per_suite/1, but this works just as well.
 all() ->
-	cowboy_test:common_all().
+	%% @todo Implement these tests for HTTP/3.
+	cowboy_test:common_all() -- [{group, h3}, {group, h3_compress}].
 
 init_per_suite(Config) ->
 	cowboy_tracer_h:set_trace_patterns(),