Support private trait aliasing

[muglug]

trait T {
  public function foo() : void {
    echo "here";
  }
}

class C {
  use T {
    foo as private traitFoo;
  }
  
  public function bar() : void {
    $this->traitFoo();
  }
}

class D extends C {
  public function bar() : void {
    $this->traitFoo(); // should fail
  }
}

Expected: Call to private method C::traitFoo from context D
Actual: No issue
https://getpsalm.org/r/695c8bd848