FR: Allow 'self' return type to allow return type changing with inheritance

还没有人认领这个 Issue。

When annotating that one class has inherited from another, there is currently no way to annotate a function that returns it's current type that the current type should change when the class is inherited. Something along these lines, or something that accomplishes the same goal would be fantastic.

```lua
---@class Foo
Foo = {}

---@return self --<-- 'self' refers to Foo so Foo.new() returns Foo
function Foo.new() end

---@class Bar : Foo
Bar = {}

local b = Bar.new() --<-- Bar.new() is inherited so the 'self' return type is now Bar
-- b should now be type Bar
```

Thanks!

从 issue 中的 Foo/Bar Lua 示例开始，跟踪 @return 注解和继承方法的解释方式。当 Bar 继承的构造函数将其结果推断为 Bar 而不是 Foo，并且涵盖所演示的行为时，即视为完成。

由索引模型根据 Issue 内容生成。