Multicast support in Direct Sockets #1

This CL adds IDL files for Multicast and necessary parameters to
UDPSocketOptions. Not everything is in place yet. cover: 1. Permission
Policy 2. Communication with real socket via mojo 3. Usage histograms 4.
Workers support 5. WPT tests (possibly).

Explainer
https://github.com/explainers-by-googlers/multicast-in-direct-sockets.
Chrome Entry https://chromestatus.com/feature/5073740211814400 Intent to
prototype
https://groups.google.com/a/chromium.org/g/blink-dev/c/ADV4FZtN4nE

The functionality is gated behind a blink flag MulticastInDirectSockets.

Bug: 398934282
Change-Id: I57e7b982269b176e29657d07f69d838e016ad55f
Low-Coverage-Reason: TESTS_IN_SEPARATE_CL
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6894978
Commit-Queue: Vlad Krot <vkrot@google.com>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Reviewed-by: Andrew Rayskiy <greengrape@google.com>
Cr-Commit-Position: refs/heads/main@{#1509508}