[Feature request] Annotation for referring to superclass

Nobody has claimed this yet.

I'm trying to add annotations to [classic](https://github.com/rxi/classic/blob/master/classic.lua), but encounter a few problems when doing so.

For example, the `super` field refers to the superclass. If I were to annotate super like this
```lua
---@class Object
---@field protected super Object
```
then subclasses will have a `super` field, but it will always refer to `Object`, instead of their superclass. The best solution I can come up with the current implementation is to set the `super` field each time a class is created.
```lua
---@class Animal : Object
---@field super Object
local Animal = Object:extend()

---@class Bird : Animal
---@field super Animal
local Bird = Object:extend()
```
This is a repetition of steps, which tells me DRY. I suggest something like a `super` annotation, which always refers to the superclass relative to which class it is being used.
```lua
---@class Object
---@field protected super super

---@class Animal : Object
local Animal = Object:extend()
-- Animal.super refers to Object

---@class Bird: Object
local Bird = Animal:extend()
-- Bird.super refers to Animal
```

Start by reviewing the annotation examples and the classic.lua inheritance model referenced in the issue. Determine where class field annotations are resolved and define how a superclass-relative annotation should behave for Object, Animal, and Bird; the issue names no LuaLS files or tests, so completion criteria need to be established before implementation.

Written by the indexing model from the issue text.