Make DnsTlsTransport's query method static

This refactor removes the need for DnsProxyListener's query hook
to call the DnsTlsTransport constructor.  This will allow us to
maintain state for longer (e.g. reusing sockets) without
increasing the complexity of DnsProxyListener.

Bug: 63448521
Test: Integration tests pass.
Change-Id: I3ec3713e188ea11b160e61d1d873469c5ad57ae7