Refactor FrameInstrumentationGenerator to handle missing VideoFrames.

If a raw `VideoFrame` is not available to when trying to generate frame
instrumentation data, still update the state with a sync messages.

This is especially important on keyframe where we've state that frame
instrumentation data must be available. Otherwise we may end up in a
state where we're unable to produce instrumentation at all for a layer.

Bug: webrtc:358039777
Change-Id: Id64e139ddcfa2bf4211aa624ec701fe6dcdcda7f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/488400
Commit-Queue: Erik Språng <sprang@webrtc.org>
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48180}