NativeFunctionInvocationFixer - PHP 8 attributes

[HypeMC]

The NativeFunctionInvocationFixer removes the leading \ from attributes when strict is set to true which breaks the code.

Config:

'native_function_invocation' => [
    'strict' => true,
],

Result:

-#[\Attribute(\Attribute::TARGET_CLASS)]
+#[Attribute(\Attribute::TARGET_CLASS)]
class Foo {}

This PR should fix the problem.

[coveralls]

Coverage increased (+0.001%) to 91.846% when pulling 54dbfc3 on HypeMC:native-function-invocation-attributes into c64d3f2 on FriendsOfPHP:2.18.

[keradus]

Thank you @HypeMC.