[CodeQuality] Add new rule to change "static::CONSTANT" to "self::CONSTANT"

[TomasVotruba]

In class that has constant in the same class, has no parent class, follwoing should be changed to self as no other constant is available.

class SomeClass
{
    private const NAME = 'cool rule';

  public function run()
  {
-   return static::NAME;
+   return self::NAME;
   }   
}

It also fixes PHPStan reports :+1:

[samsonasik]

It seems only works on private constant, on protected/public, it still needed, see

https://3v4l.org/rPYm0 vs https://3v4l.org/80571

[samsonasik]

Actually, there is already rule ConvertStaticPrivateConstantToSelfRector for that, see https://getrector.com/demo/5c3ff3fc-8b61-45d1-acab-2bb3f974f3af

[samsonasik]

I added ability to change into self on final class:

• https://github.com/rectorphp/rector-src/pull/6295

[TomasVotruba]

Thank you 🙏