Convert AsyncDnsResolver to use absl::AnyInvocable

Bug: webrtc:12598
Change-Id: I0950231d6de7cf53116a573dcd97a3cf5514946c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/318400
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40670}

api/BUILD.gn

diff --git a/api/BUILD.gn b/api/BUILD.gn
index b2a7947..f2d10ec 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -410,6 +410,7 @@
     "../rtc_base:socket_address",
     "../rtc_base/system:rtc_export",
   ]
+  absl_deps = [ "//third_party/abseil-cpp/absl/functional:any_invocable" ]
 }
 
 rtc_source_set("wrapping_async_dns_resolver") {