- ReconfigureDNS wasn't returning the old servers; made it void instead
(the Apple code can just store a copy of the original upstream
servers instead).
- Reconfiguring DNS reset the unbound context but didn't replace it, so
a Down()/Up() would crash.
- Simplify Resolver() destructor to just call Down(), and make it final
just so that no one tries to inherit from us (so that calling a
virtual function from the destructor is safe).
- Rename CancelPendingQueries() to Down(); the former cancelled but also
shut down the object, so the name seemed a bit misleading.
- Rename SetInternalState in Resolver_Base to ResetResolver, so that we
aren't conflicting with ResetInternalState from Endpoint (which was a
problem because TunEndpoint inherited from both; it could be resolved
through the different argument type if we removed the default, but
that seems gross).
- Make Resolver use a bare unbound context pointer rather than a
shared_ptr; since Resolver (now) entirely manages it already we don't
need an extra management layer, and it saves a bunch of `.get()`s.
Apple supports anything here that Clang supports and should have them
set the same as everywhere else.
Most importantly this gives apple the -Wno-deprecated-declarations flag
which has been driving me nuts on macos.
This also version-gates the -Wno-deprecated-declarations so that it
will turn on again when we bump the version beyond .10.
When we enable/disable exit mode on this restarts the unbound DNS
responder with the DNS trampoline (or restores upstream, when disabling)
to properly route DNS requests through the tunnel (because libunbound's
direct requests don't get tunneled because unbound is inside the network
extension).
