yuniffi: Migrate to new API set

[okuoku]

Move (yuni ffi *) functionalities to separate libraries because some of these are not FFI-specific.

Unified structure APIs (yuni core)

• No short names: new yuni-set! yuni-ref procedures
• No Scheme core object support
• Common API for 3 types of object, symbol addressed: dynamic tables(JSON etc), buffers, bytevectors, hashtables (require eq-hashtable->yuni etc)

We don't see any performance benefit over defining core ref/set! as syntax; future Yuni will use inline-hints.

Buffer APIs (yuni buffers)

• 3 types of buffer: Transient / Pinnable bytevector / Foreign
• Unified raw integer/IEEE-float access, aligned/unaligned

Transient buffer is alloca equivalent. MIT/GNU Scheme 10 or later has real FFI thus we no longer need special handling for them.

Structure pack/unpack (yuni pack)

• Structure definition
• Core value interpolation: byte-length, count, zero, padding
• Bitfield pack/unpack
• Symbol-as-enum features
• Structure/Parameter templates

C calling primitives (yuni ffi nccc)

• NCCC(Normalized C Calling Convention): Yuni will only support following function signature(s) C stub generator will generate wrapper using API description and wrapper will be shared with Yuni implementations, including non-Scheme ones
• Callback trampoline management - Callback to Scheme might be an optional feature though
• Pointer patching - replace bytevector/buffer references into pointers for API parameters
• ABI backfilling - Fetch actual structure layout from precompiled static bindings for (yuni pack)

(NCCCv0)

void some_api(uint64_t* in, int in_len, uint64_t* out, int out_len);

(NCCCv1 - TBD)