Previously, fc reflection generated visitor infrastructure capable of
visiting each field of a struct; however, this is only useful for run-
time operations on structures. No compile-time information was preserved
about the fields of a struct, making compile-time introspection of types
impossible.
Now FC reflection generates rich compile-time information about the
members of structs, including types, names, and structure, allowing
code to be written to explore types in detail at compile-time and fetch
arbitrary fields at runtime without needing to iterate over the unwanted
fields.
To make this a reality, a new `typelist` type was added to store this
compile-time information. This type is also useful within the context of
`static_variant`, as SV previously used implementation detail types in a
private namespace to provide this functionality. Now `static_variant`
uses the reusable functionality of `typelist` to operate, dramatically
reducing the amount of code dedicated to `static_variant` and also
making `static_variant` types more flexible to work with since their
infrastructure is now based on the `typelist` public interface.
