Replace stack_pop_N with stack_pop<N>

```rust
fn stack_pop<'ctx, const N: usize>(
    bctx: &BuildCtx<'ctx, '_>,
) -> Result<[Value<'ctx>; N], Error> {
    std::array::try_from_fn(|_| call_stack_pop(bctx))
}
```

Destructure like:

```rust
let [a, b, c] = stack_pop<'ctx, 3>(bctx);
```

Delete StackPopN types. 