Include Sframe library in libwebrtc

# Summary

This CL pulls Chromium's `third_party/sframe` library into WebRTC as a
new third-party dependency. The library provides the core SFrame (RFC
9605) cryptographic primitives — key derivation, AEAD
encryption/decryption, header serialization, and counter management —
that WebRTC's upcoming end-to-end media encryption pipeline will build
on top of.

Bug: webrtc:479862368
Change-Id: Ib72d0cfa6cd5ed24be1e671fde0b124b5284d59d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/474364
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47834}