Mark FU packets with type between kBlaWLp and kRsvIrapVcl23 as key frames. This behavior aligns with AP and single NALU. Bug: webrtc:13485 Change-Id: I51762e89ebb4829b50524d9f5476f2d5d9c093f7 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/338860 Reviewed-by: Philip Eliasson <philipel@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41764}