video: add EncoderInfo CPU overuse flag and aggregate in simulcast

enable_cpu_overuse_detection=true by default, even when all sub-encoders
disabled it.
sub-encoder's value, so CPU overuse detection only runs when at least
one encoder opts in.

Before: In multi-encoder simulcast, SimulcastEncoderAdapter returned
After: The adapter initializes the flag to false and ORs each
Bug: webrtc:42225459
Change-Id: Ib5ae02408854507364bb2c5041e3aea61c3b0ad8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/443381
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46933}