Reland "Add an active ICE controller that wraps a legacy controller (#7/n)"

This is a reland of commit 6326c9c201c7331d68c9beb0a93f6f6e21063cd2

Original change's description:
> Add an active ICE controller that wraps a legacy controller (#7/n)
>
> The wrapping ICE controller will allow existing ICE controller implementations to migrate to the active interface, and eventually deprecate the legacy interface.
>
> Follow-up CL has unit tests for P2PTransportChannel using the new wrapping controller.
>
> Bug: webrtc:14367, webrtc:14131
> Change-Id: I6c517449ff1e503e8268a7ef91afda793723fdeb
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/275302
> Reviewed-by: Per Kjellander <perkj@webrtc.org>
> Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
> Commit-Queue: Sameer Vijaykar <samvi@google.com>
> Cr-Commit-Position: refs/heads/main@{#38130}

Bug: webrtc:14367, webrtc:14131
Change-Id: I5662595db1df8c06b3acac9b39749f236906fa7e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/276044
Auto-Submit: Sameer Vijaykar <samvi@google.com>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38149}
diff --git a/api/ice_transport_interface.h b/api/ice_transport_interface.h
index cd6ada8..2ec41aa 100644
--- a/api/ice_transport_interface.h
+++ b/api/ice_transport_interface.h
@@ -99,8 +99,10 @@
   //      constructed and used.
   //
   //   2. If the field trial is enabled
-  //      - then an active ICE controller factory must be supplied and is used.
-  //      - the legacy ICE controller factory is not used in this case.
+  //      a. If an active ICE controller factory is supplied, it is used and
+  //      the legacy ICE controller factory is not used.
+  //      b. If not, a default active ICE controller is used, wrapping over the
+  //      supplied or the default legacy ICE controller.
   void set_active_ice_controller_factory(
       cricket::ActiveIceControllerFactoryInterface*
           active_ice_controller_factory) {