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

還沒有人認領這個 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!

從 issue 中的 Foo/Bar Lua 範例開始，追蹤 @return 註解和繼承方法的解讀方式。當 Bar 繼承的建構函式將其結果推斷為 Bar 而不是 Foo，並且涵蓋所示範的行為時，即視為完成。

由索引模型根據 Issue 內容生成。