[php-src] Issue #11377: [SPL] Add some missed methods to `SplFixedArray`

Issue: https://github.com/php/php-src/issues/11377 Author: alirezasalehizadeh ### Description ### Description It seems that some missing methods can be added to ‍‍‍‍SplFixedArray class which can be useful: 1- Push or Append method: By default for add a new element to SplFixedArray we can do this: ```php // Initialize the array with a fixed length $array = new SplFixedArray(3); // Add a new element to array $array[1] = 2; var_dump($array[1]); // int(2) ``` We can have a missed push, add or append method like this: ```php // Initialize the array with a fixed length $array = new SplFixedArray(3); // Add a new element to array $array->push(1, 2); var_dump($array[1]); // int(2) ``` 2- each method: Like array_map, this can be a easy way to work with array elements like this: ```php // Initialize the array with a fixed length $array = new SplFixedArray(2); // Add new elements to array $array[0] = 1; $array[1] = 2; // Applies the callback to the elements of the array $newArr = $array->each(function($el){ return $el + 1; }); var_dump($newArr); /** array(2) { [0]=> int(2) [1]=> int(3) } */ ``` In [QuickArray](https://github.com/alirezasalehizadeh/QuickArray) im use this methods in use.