The metadata accessor for a variadic generic type takes as arguments
packs of metadata records and witness tables, and each such pack is
passed in a buffer. So any such accessor is not correctly annotated
`memory(none)`.
rdar://161606892
This removes the "optimization" where a function type, metatype or
tuple type was split up into structural components, because it seems
that in general we need this structural type metadata again.
Similarly, this no longer tries to split up dependent concrete
conformances and instead passes the witness table in the context.
This makes the context larger potentially, but it avoids calls to
metadata access functions and swift_getWitnessTable() every time the
closure is invoked.
Metadata accessors are dependent on prespecializations of the metadata
of generic, in-module types. Those prespecializations are themselves
dependent on usages of the types in functions. Consequently, the
accessors must be emitted after all the functions are emitted.
