Reland "Partial frame capture API part 1"

Reland with fixes to undefined behavior.

Define new optional struct in VideoFrame to signal that the frame is a
changed part of a whole picture and add a flag to signal that partial
update may be issued by the VideoFrame source.

Also, fix too strict assumptions in FrameBuffers PasteFrom methods.
Also, add ability to set a new buffer in video frame.

Original Reviewed-on: https://webrtc-review.googlesource.com/c/120405

Bug: webrtc:10152
Change-Id: I85790dfc7cec2f23abfe9d6cd18dc76a0c343bc0
Reviewed-on: https://webrtc-review.googlesource.com/c/120780
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26493}