net/tsdial, ipn/ipnlocal: stop using netmap.NetworkMap in Dialer

tsdial.Dialer.SetNetMap rebuilt an O(n peers) map of MagicDNS names on
every netmap change. As we move toward per-peer incremental deltas,
this becomes quadratic. This removes it and replaces it with
SetResolveMagicDNS, a callback into LocalBackend that looks up
hostnames from nodeBackend's new nodeByName index (populated alongside
nodeByAddr/nodeByKey on both full and delta paths). The index stores
both FQDNs and short names as keys.

This is the same treatment applied to netlog (8f210454d), wglog
(988b0905b), and drive (1d6989408): stop pushing *netmap.NetworkMap
into subsystems and instead have them pull from LocalBackend's live
data via callbacks.

Updates #12542

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I24557ab0c8a27636e08e4779bcfd3ec633db0a78

cmd/k8s-operator/depaware.txt

@@ -849,7 +849,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
         tailscale.com/types/lazy                                     from tailscale.com/ipn/ipnlocal+
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/ipn/ipnlocal+
-        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
+        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext+
         tailscale.com/types/netlogfunc                               from tailscale.com/net/tstun+
         tailscale.com/types/netlogtype                               from tailscale.com/wgengine/netlog
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+

cmd/tailscaled/depaware-min.txt

@@ -140,7 +140,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/lazy                                     from tailscale.com/hostinfo+
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/cmd/tailscaled+
-        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
+        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext+
         tailscale.com/types/netlogfunc                               from tailscale.com/net/tstun+
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
         tailscale.com/types/nettype                                  from tailscale.com/net/batching+

cmd/tailscaled/depaware-minbox.txt

@@ -159,7 +159,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/lazy                                     from tailscale.com/hostinfo+
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/cmd/tailscaled+
-        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
+        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext+
         tailscale.com/types/netlogfunc                               from tailscale.com/net/tstun+
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
         tailscale.com/types/nettype                                  from tailscale.com/net/batching+

cmd/tailscaled/depaware.txt

@@ -426,7 +426,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/lazy                                     from tailscale.com/ipn/ipnlocal+
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/cmd/tailscaled+
-        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
+        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext+
         tailscale.com/types/netlogfunc                               from tailscale.com/net/tstun+
         tailscale.com/types/netlogtype                               from tailscale.com/wgengine/netlog
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+

cmd/tsidp/depaware.txt

@@ -247,7 +247,7 @@ tailscale.com/cmd/tsidp dependencies: (generated by github.com/tailscale/depawar
         tailscale.com/types/lazy                                     from tailscale.com/cmd/tsidp+
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/ipn/ipnlocal+
-        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
+        tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext+
         tailscale.com/types/netlogfunc                               from tailscale.com/net/tstun+
         tailscale.com/types/netlogtype                               from tailscale.com/wgengine/netlog
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+