net: a better builtin DNS stub resolver

[mikioh]

This is a meta bug for tracking the status of the issues regarding builtin DNS stub resolver.

• Refabrication
  • proposal: x/net/dns, vendor/golang.org/x/net/dns: new package #16218
• Transport
  • net: issue with DNS response > 512 bytes (cannot unmarshal DNS message) #21160
  • net: better DNS transport for builtin DNS stub resolver #23866
  • net: don't keep reading from UDP resolver after truncated packet #23873
  • net: support DNS-over-HTTPS #27552
• Labels
  • net: reject Lookup("www.google.com..") on all systems #7122
  • net: LookupSRV and search domains when name is empty #9391
  • net: mishandling of dotted labels in domain names #10631
  • net: target domain names in SRV records should not be compressed #10622
  • net: isDomainName rejects valid domains #17659
  • net: LookupHost IDN support #22782
  • proposal: net: add support for "let localhost be localhost" #22826
• RRs
  • net: go 1.11 DNS client incompatible with SRV records from kube-dns #27546
• Error handling
  • net: dns lookup sometimes fails with "no such host" when there are too many open files #18588
• Options
  • net: add EDNS0 support to builtin DNS stub resolver #6464
  • net: validate DNSSEC in Go's DNS resolver #13279
• Testing
  • net: more complete DNS stub resolver tests for uncommon scenarios #13295