EncoderStateObserver: Take required info in OnEncodedImage()

This CL changes EncoderStateObserver::OnEncodedFrame() interface.
First, the function is renamed to OnEncodedImage() to be consistent to
EncodedImageCallback. Second, the argument takes the required
information for state observation, not webrtc::EncodedImage.

Bug: b:320555128
Test: blink_platform_unittests
Change-Id: I38861f2ccc37d8e9f7cf6fa4e45bccc8856016bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5679903
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Erik Språng <sprang@chromium.org>
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1324617}