template <typename... ExtraItems>
struct Add
Defined at line 403 of file ../../zircon/kernel/phys/lib/boot-shim/include/lib/boot-shim/boot-shim.h
`Add` will generate a `struct` with a `type` member whose type is `StandardBootShim`
instantiated with the the union of `Items` and `ExtraItems`.
`ExtraItems` must not contain any item already present in `Items`, that is, they must
not overlap.