Register PropertyExistsWithoutAssertRector in the composer-based set

[TomasVotruba]

Follow-up to #760, which was merged before this fix reached the branch.

PropertyExistsWithoutAssertRector was registered only in config/sets/phpunit100.php. #760 removed that file, so the rule is currently in no set at all — it can only be reached by adding it by hand.

The rule already implements ComposerPackageConstraintInterface with a >=10.0 constraint, and its own docblock says "inherited from the PHPUnit 10.0 set", so composer-based.php is where it belongs.

The overlap this surfaced

Registering it exposed a conflict that already existed in the old phpunit100.php, where both were registered side by side — it was simply never covered by a fixture. The rule and the set's >=10.1 RenameMethodRector both claim assertObjectHasAttribute():

	produces
RenameMethodRector, >=10.1	$this->assertObjectHasProperty('someProperty', new stdClass())
PropertyExistsWithoutAssertRector	$this->assertTrue(property_exists(new stdClass(), 'someProperty'))

Resolved in favour of the rename, since these two methods are the only ones in the rule's map that have a direct PHPUnit replacement:

-$this->assertObjectHasAttribute('someProperty', new stdClass());
+$this->assertObjectHasProperty('someProperty', new stdClass());

So assertObjectHasAttribute and assertObjectNotHasAttribute are dropped from the rule's map, and its fixture becomes a skip case that asserts they are left alone.

What the rule still does

The remaining 7 methods have no direct replacement, so converting them to property_exists() stays the only upgrade path:

-$this->assertClassHasAttribute('property', 'stdClass');
+$this->assertTrue(property_exists('stdClass', 'property'));