This commit removes "Deno.core" namespace. It is strictly private API
that has no stability guarantees, we were supposed to remove it long time ago.
Co-authored-by: Yoshiya Hinosawa <stibium121@gmail.com>
V8's JIT can do a better job knowing the argument count and also enable
fast call path (in future).
This also lets us call async ops without `opAsync`:
```js
const { ops } = Deno.core;
await ops.op_void_async();
```
this patch: 4405286 ops/sec
main: 3508771 ops/sec
