Update PHP-Parser from 4.3.0 to 4.9.0

[TysonAndre]

PHP-Parser 4.3.0 failed to recognize that the match keyword could be
used as a class constant name.
4.9.0 also adds support for keywords in namespaced names.
See https://github.com/nikic/PHP-Parser/releases

So forcing regeneration of spl_iterators.stub.php failed.

PECL extensions using gen_stub.php would also be affected
by the same issue for those keywords.

// PHP 4.3.0 is not aware of the T_MATCH token
ext/spl/spl_iterators.stub.php
    public function __construct(Iterator $iterator, string $regex,
    int $mode = self::MATCH, int $flags = 0, int $preg_flags = 0) {}

Testing: I successfully regenerated stubs by setting forceRegeneration to true
and running touch **/*.stub.php; make.
The stubs did not change, as expected.

CC @nikic @kocsismate @cmb69

[kocsismate]

@TysonAndre Thanks! This upgrade will also allow us to remove the hack from gen_stubs that was introduced for the mixed type.