support for `(partial)` class atrribute

[lewis6991]

--- @class A
--- @field b string

--- @class (partial) B: A

--- @type A
local a = {} -- missing fields

--- @type B
local b = {} -- correct

--- @param a A
function foo(a) end -- missing fields

--- @param b B
function bar(b) end -- correct

[CppCXY]

our partial class has designed like C# partial class，I think you just need Partial<T> class

[lewis6991]

Would it be worth supporting (partial) to be compatible with LuaLS? I want Neovim to move over to emmylua, but that will take some time, so need this to be as compatible with LuaLS as possible.

[CppCXY]

the partial feature of luals is also design by me。I donot remember this feature。
The initial partial enum was designed according to the functionality I mentioned earlier. The later partial class, added via someone else's pull request, might not have aligned with my original design intent.

[lewis6991]

As far as I understand it, @class (partial) B : A just means all fields of B including inherited fields can be nil. I would also expect that.

---@class (partial) A

---@class B: A

To be equivalent to:

---@class B : Partial<A>

And:

---@class A

---@class (partial) B: A

To be equivalent to:

---@alias B Partial<A>

Except that with this, we cannot add fields to B.

Is there anything there that you disagree with?