Suggest/complete primitive indexed fields

[Benjamin-Dobell]

Presently only named fields are suggested/completed.

For example:

---@class Vector
---@field x number
---@field y number
---@field [1] number
---@field [2] number

---@type Vector
local myVector

myVector.--<cursor here>

This will display a completion prompt that only includes the members x and y. However, it could also suggest [1] and [2] and upon completion delete the period.

Additionally, index expressions using brackets could similar be completed e.g.

myVector[--<cursor here>

If we're going to be completing all fields in brackets then we'll presumably want to prioritise primitive indexed fields over regular named fields and vice versa when completing fields after a period.

See #27 for initial report.

Considerations / Additional Thoughts

We're only going to be completing primitives, but what about aliases? e.g.

---@alias Color "Red" | "Blue"

---@class Palette
---@field [Color] number

---@type Palette
local palette

palette.--<cursor here>

Should we suggest "Red" and "Blue"?

We certainly can, however completion prompts ought to be very responsive, so minimising work is a good idea 😕

[ChloeDawn]

It would also be useful to have aliases auto-complete when used as an explicit argument to a function

---@alias Color "Red" | "Blue"

---@param color Color
function setColor(color) end

setColor(" --<suggest Color aliases>

---@param color Color | string
function setCustomColor(color) end

setCustomColor(" --<also suggest Color aliases>