De-genericize one axis of storage buffers to speed up compilation time
of stdlib and user code. Publish the rest as ABI, since we're out of
time to reevaluate the design.
Aggressively remove all `@inlinable` from any function that's
`@inline(never)` to see the impact.
`@inlinable @inline(never)` is a potential code smell. While it might
expose some optimization and specialization opportunities to the
optimizer, it's most commonly a sign that more thought is needed.
In theory there could be a "fixed-layout" enum that's not exhaustive
but promises not to add any more cases with payloads, but we don't
need that distinction today.
(Note that @objc enums are still "fixed-layout" in the actual sense of
"having a compile-time known layout". There's just no special way to
spell that.)
The best high-level APIs for decoding/transcoding are still under active
investigation. It's likely we want more views. Therefore, leave
de-underscored/public only the lowest-level APIs for now.
This is a follow-up fix for making struct constructors inline(__always) in
155db0a4bd: Let Character literals, which fit into 64 bits, be folded into a single integer constant.
and
d8f1caf4a6: Inline all the new low-level bits
If we decide that this structs should not have fixed layout we must re-evaluate the performance difference of not being able to inline
the struct constructors.
