This CL implements `ChangeResolution()` to let `Y4mFrameGenerator`
generate I420 frame with resolution other than y4m input by scaling. The
code is mostly copied from `IvfVideoFrameGenerator`.
The test case is also added for this change.
Bug: webrtc:15210
Change-Id: I690e427a545a72d93ed39b77fd0f602054a30508
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/311521
Commit-Queue: Jianhui J Dai <jianhui.j.dai@intel.com>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40426}
9e5defcf74