This patch returns an empty Optional<...> instead of an Error for
Core::System::getgrname and Core::System::getpwnam if we can't find a
matching group or user entry.
It also updates the 'chown' utility to support this new behavior.
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 *
