feat(extgen): add support for callable in parameters

[alexandre-daubois]

Depends on #1724. 50e2a65 should be reviewed independently.

Allows to write such code:

// export_php:function my_array_map(array $data, callable $callback): array
func my_array_map(arr *C.zval, callback *C.zval) unsafe.Pointer {
	goArr := frankenphp.GoArray(unsafe.Pointer(arr))
	result := &frankenphp.Array{}

	for i := uint32(0); i < goArr.Len(); i++ {
		key, value := goArr.At(i)

                // Magic is here!
		callbackResult := frankenphp.CallPHPCallable(unsafe.Pointer(callback), []interface{}{value})

		if key.Type == frankenphp.PHPIntKey {
			result.SetInt(key.Int, callbackResult)
		} else {
			result.SetString(key.Str, callbackResult)
		}
	}

	return frankenphp.PHPArray(result)
}

$strArray = ['a' => 'hello', 'b' => 'world', 'c' => 'php'];
var_dump(my_array_map($strArray, 'strtoupper'));

$arr = [1, 2, 3, 4, [5, 6]];
var_dump(my_array_map($arr, function($item) {
    if (is_array($item)) {
        return my_array_map($item, function($subItem) {
            return $subItem * 2;
        });
    }

    return $item * 3;
}));

/*
Output:

array(3) {
  ["a"]=>
  string(5) "HELLO"
  ["b"]=>
  string(5) "WORLD"
  ["c"]=>
  string(3) "PHP"
}
array(5) {
  [0]=>
  int(3)
  [1]=>
  int(6)
  [2]=>
  int(9)
  [3]=>
  int(12)
  [4]=>
  array(2) {
    [0]=>
    int(10)
    [1]=>
    int(12)
  }
}
*/

TODO: fix support on methods

[withinboredom]

IIRC, callables are not callable from arbitrary threads (I've tried this!). Meaning if you hold a callable reference and try to call it from another php thread, it will crash. This probably just needs to be documented for authors.

Objects are the same IIRC.

HOWEVER, opcache will copy all these pointers into a shared arena during compilation, so if you have opcache turned on, it might work.