Allow moving the class, add required RTC_EXPORTs Bug: webrtc:347737882 Change-Id: Iac14e6f62adfa13ff1e757918a2f92009f5be36f Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/361760 Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org> Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Cr-Commit-Position: refs/heads/main@{#42962}