fix(types/unstable): better type hints for Deno.dlopen (close: #16873)

[ahaoboy]

close #16873
Use magic code wrap parameters type and get more accurate return type

  type Cast<A, B> = A extends B ? A : B;
  type Const<T> = Cast<
    T,
    | (T extends string | number | bigint | boolean ? T : never)
    | { [K in keyof T]: Const<T[K]> }
    | []
  >;
declare function f<T>(arg: Const<T>): T;


let r = f({
  a: {
    b: 1,
    c: "2",
  },
});

[CLAassistant]

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[littledivy]

Thank you for the PR @ahaoboy

Can you add type tests in test_ffi/tests/ffi_types.ts ?

[ahaoboy]

@littledivy
I remove all as const in test_ffi/tests/ffi_types.ts, This tick also works for both UnsafeCallback and UnsafeFnPointer.