Add defaulted move constructors for some types that just got copy constructors

They can all benefit from moving, since they contain std::string and
std::vector. We intended to add these in
https://codereview.webrtc.org/1896953004/, but got compiler errors we
couldn't make sense of, so we skipped them. It turns out that what the
compiler was complaining about was that when we said we'd have a
user-defined move constructor, it stopped generating a copy assignment
operator for us. This CL solves the problem by outfitting the types
with defaulted copy and move assignment operators too.

Review URL: https://codereview.webrtc.org/1899173002

Cr-Commit-Position: refs/heads/master@{#12469}