Add quickfix for bad visibility modifiers

[Wilfred]

Sample bad code:

class MyParent {
  public function foo(): void {}
}

class MyChild extends MyParent {
  // autofix: public function
  protected function foo(): void {}
}

After applying the quickfix, the visibility should match the parent class.

class MyParent {
  public function foo(): void {}
}

class MyChild extends MyParent {
  public function foo(): void {}
}