feat: clearly indicate which resolver we're using (#885)

See what we documented at https://github.com/ooni/spec/pull/257

Reference issue: https://github.com/ooni/probe/issues/2238

See also the related ooni/spec PR: https://github.com/ooni/spec/pull/257

See also https://github.com/ooni/probe/issues/2237

While there, bump webconnectivity@v0.5 version because this change
has an impact onto the generated data format.

The drop in coverage is unavoidable because we've written some
tests for `measurex` to ensure we deal with DNS resolvers and transport
names correctly depending on the splitting policy we use.

(However, `measurex` is only used for the `tor` experiment and, per
the step-by-step design document, new experiments should use
`measurexlite` instead, so this is hopefully fine(TM).)

While there, fix a broken integration test that does not run in `-short` mode.

internal/netxlite/dnsovergetaddrinfo.go

@@ -24,6 +24,11 @@ type dnsOverGetaddrinfoTransport struct {
 	testableLookupANY func(ctx context.Context, domain string) ([]string, string, error)
 }
 
+// NewDNSOverGetaddrinfoTransport creates a new dns-over-getaddrinfo transport.
+func NewDNSOverGetaddrinfoTransport() model.DNSTransport {
+	return &dnsOverGetaddrinfoTransport{}
+}
+
 var _ model.DNSTransport = &dnsOverGetaddrinfoTransport{}
 
 func (txp *dnsOverGetaddrinfoTransport) RoundTrip(