[Feature Request] Allow mark any as @enum

Issue Description

---@enum Type
local Type = {
	A = 1,
	B = 2,
	-- ...
}

---@return {[string]: integer}
function Generate_enum()
	return {}
end

---@enum (partial) Type
local Type2 = {}

for k, v in pairs(Generate_enum()) do
	Type2[k] = v
end

---@enum (partial) Type
local Type3 = Generate_enum()

The point is to achieve the same behavior for Type3 as for Type2.

Start by reproducing the issue's Lua examples and inspect the language server's existing @enum handling and type inference for assignments. Compare Type2 and Type3, then add coverage so a partial enum assigned directly from Generate_enum() receives the same behavior as the incremental assignment; done means their diagnostics and type information match.