Fix parsing classes containing anonymous classes

[stevebauman]

This PR patches a bug I discovered when it parses a class containing an anonymous class.

When one is encountered, a FQCN is returned in the result with the basename of ( or {, after the FQCN of the one that contained the anonymous class.

For example, if you remove the isAnonymousClass method included in this PR, the below entry is returned in the class list:

$found = Discover::in(__DIR__ . '/Fakes')->get();

var_dump($found); // [..., "Spatie\StructureDiscoverer\Tests\Fakes\(", ...]

I've added a test case to ensure this is resolved, and have also added a case for ensuring files containing multiple class names can be returned as well.

[freekmurze]

Thank you!