Make Opus encoder configurations friendly to move-only types

Refactors AudioEncoderOpusConfig, AudioDecoderOpusConfig and
AudioEncoderMultiChannelOpusConfig to be compatible with move-only types
such as AnyInvocable.

This includes updates to factory methods, implementation classes, and
unit tests to use std::move where appropriate.

Bug: none
Change-Id: I173708c1692efdc61cd3027d1b8e7ee35a046200
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/436640
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46584}