Validate WASI import arity before binding host functions

[aizu-m]

ASan on wasm-interp --wasi, running a valid module that under-declares a WASI import:

ERROR: AddressSanitizer: heap-buffer-overflow ... READ of size 8
  #1 wabt::interp::Value::CheckType(wabt::Type) const          interp.h:596
  #2 unsigned long long wabt::interp::Value::Get<...>() const  interp-inl.h:457
  #3 (anon)::WasiInstance::clock_time_get(...)                 interp-wasi.cc:198
  #4 (anon)::clock_time_get(...)                               wasi_api.def:26
  ...
  #13 wabt::interp::Thread::DoCall(...)                        interp.cc:2209
  #19 wabt::interp::WasiRunStart(...)                          interp-wasi.cc:750

Found this fuzzing wasm-interp --wasi with hand-built modules.

WasiBindImports binds each import to its host callback by name and keeps the
func type the module declared. There is a // TODO(sbc): Validate signatures
right next to it. Thread::DoCall then sizes the params/results vectors
from that declared type, but every callback indexes params[]/results[] by
the arity of the real WASI function.

So a module that imports clock_time_get as (i32) -> i32 instead of
(i32 i64 i32) -> i32 still validates, and the call reads params[1] past a
one-element vector. The *_get handlers also do results[0].Set<...>() on an
empty results, so a mis-declared result count is an out-of-bounds write as
well. Both are reachable from an untrusted module through wasm-interp --wasi.

Fix carries each function's (num_params, num_results) in wasi_api.def and
rejects a mismatched import before HostFunc::New, so the arity check fails at
bind time rather than at the out-of-bounds access. Arity only, deliberately:
some callbacks read i64 params as u32 (path_open rights, fd_seek offset),
so checking the types here would reject conforming modules. The declared arity
is fixed by the WASI ABI, so valid modules are unaffected.

Test declares clock_time_get with the wrong arity and expects the bind-time
rejection; the existing test/wasi cases still pass. wasm-interp --wasi
needs -DWITH_WASI=ON.

[zherczeg]

In #2842, it was recommended to remove the entire wasi support form wabt. The 0.1 is outdated, and newer ones require component support (#2695).