Add move operations to VideoEncoder::EncoderInfo

EncoderInfo declares a copy constructor and a destructor, so it has no
implicit move operations, and std::move on an EncoderInfo copies it.
For example, the EncoderContext constructor in SimulcastEncoderAdapter
and the EncoderSettings constructor take EncoderInfo by value and move
it into a member, which made a copy.

Add a defaulted move constructor and move assignment operator, and
declare the copy assignment operator, which declaring a move
constructor would otherwise delete. Like the existing copy constructor
and destructor, they are defaulted out of line.

Also move the primary and fallback infos into the new EncoderContext in
SimulcastEncoderAdapter::FetchOrCreateEncoderContext, as they are not
used afterwards. Creating an encoder context now copies EncoderInfo
once instead of six times.

Bug: webrtc:374845009
Change-Id: I77cd7211314a62fd12a871e4b88d081ab858bbb7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/507722
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48816}