An explicit move constructor is required to null-out the moved-from
directory descriptor. Otherwise, we would call closedir() twice when
using ErrorOr<DirIterator>::release_value().
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
