Resolves shadowing warnings that aren't in a particularly large
subsection of core. Brings us closer to turning -Wshadow into an error.
All that remains now is for cases in the kernel (left untouched for now
since a big change by bunnei is pending), and a few left over in the
service code (will be tackled next).
Allows some implementations to avoid completely zeroing out the internal
buffer of the optional, and instead only set the validity byte within
the structure.
This also makes it consistent how we return empty optionals.
