Template Annotation

I love the new missing-fields diagnostic! It is super helpful to guarantee safety especially for function arguments (though its usefullness in my repo has stagnated slightly due to https://github.com/LuaLS/lua-language-server/issues/2214)

However, it does come into conflict with something I do in a few places where I specifically set a type annotation for the autocomplete where the data in the table is initialized later in a meta_table (or the data is only every accessible through the meta_table).

---@type WeaponsUnitData
Weapons.unit = {}

setmetatable(Weapons.unit, Metatable.unit_metatable())

With the new missing-fields diagnostic I get a warning here, that Weapons.unit doesn't contain all of the fields on WeaponsUnitData. I was wondering with the missing-fields diagnostic we could get a ---@template annotation which could describe the shape of a table without having to define all of the fields on it. (As a cleaner alternative to having to do ---@diagnostic disable-next-line: missing-fields in a bunch of places). I am sure other people were also using tables in other weird ways before as well, this would allow an easy transition for them.

Start with the existing missing-fields diagnostic and the annotation handling involved in ---@type. Determine how a ---@template annotation could describe a table shape without requiring every field, then verify that the example using Weapons.unit no longer produces the warning while normal missing-field checks remain intact.