Enum attrs bi-directional mapping

[vallode]

Enum attributes can be access either via the key or the value of the corresponding enum, right now we are only using the value. This results in some annoying behaviour:

---@type tiletype
local ttype = dfhack.maps.getTileType(engraving.pos)
local tileattrs = df.tiletype.attrs[ttype] -- Cast as `unknown` even though this is a valid index.

The biggest issue is going to be figuring out how to do this without doubling the size of enums (again):

---@field FrozenRampTrackNEW { caption: "ice ramp track NEW", shape: "RAMP", material: "FROZEN_LIQUID", variant: "NONE", special: "TRACK", direction: "NEW" }```

Would change into:

---@field FrozenRampTrackNEW { caption: "ice ramp track NEW", shape: "RAMP", material: "FROZEN_LIQUID", variant: "NONE", special: "TRACK", direction: "NEW" }
---@field [677] { caption: "ice ramp track NEW", shape: "RAMP", material: "FROZEN_LIQUID", variant: "NONE", special: "TRACK", direction: "NEW" }

For enums with hundreds of attributes, it is less than ideal.

[vallode]

Even more annoyingly, it looks like accessing known class fields by a known integer variable is unsupported in LuaLS:

---@class Foo
---@field [0] "I am a string"
local foo

local bar = 0

local test = foo[bar] -- This _should_ result in test being known, but it is marked as "unknown" instead.