…ddEmptyDir()

Now, the .phar directory is a magic dir for phar files, and in phar::addEmptyDir(), users couldn't create a dir naming .phar

The implementation is:
```c
	if (zend_string_starts_with_literal(dir_name, ".phar")) {
		zend_throw_exception_ex(spl_ce_BadMethodCallException, 0, "Cannot create a directory in magic \".phar\" directory");
		RETURN_THROWS();
```
This has two bugs.

Firstly, people can use /.phar to create the .phar dir. The leading / will be ignored. (no need to concern about ../ though, it will be ignored.)

```php
<?php
  $phar = new Phar(__DIR__ . '/test.phar', 0, 'test.phar');
  $phar->addEmptyDir('/.phar');
  var_dump(is_dir('phar://' . __DIR__ . '/test.phar/.phar'));
```
Will return true with the .phar dir created, while if the dir is .phar it will raise an error.

Secondly, it only matches the prefix. That means, /.pharxxx will not be allowed to create, which is not a magic dir.

```php
<?php
  $phar = new Phar(__DIR__ . '/test.phar', 0, 'test.phar');
  $phar->addEmptyDir('.pharx');
```
This will raise an error.
```
PHP Fatal error:  Uncaught BadMethodCallException: Cannot create a directory in magic ".phar" directory in C:\Users\admin\Desktop\bench.php:3
```
This PR fix both by 1. adding a trailing check of the path to make .pharx valid 2. adding a check to /.phar

Closes phpGH-22146.