[Feature request] Add a pseudo-type for custom require-like functions

Nobody has claimed this yet.

I think it would be useful to have something like a `Require`-type. This type would take a literal string type `T` and evaluate as the same type that calling `require(modname: T)` would. This way, a wrapper around `require` could easily be built like this:

```lua
--- Require a module, throwing an error if it returned `true` (meaning that you
--- probably forgot to actually return something from it).
---@generic T : string
---@param module_name T
---@return Require module -- <-- Note the use of `Require`
local function checked_require(module_name)
assert(type(module_name) == "string", "The `module_name` must be a string!")

local module = require(module_name)

assert(
module ~= true,
string.format(
"Could not import module: `require(%q)` returned `true`!",
module_name
)
)

return module
end

--------------------------------------------------------------------------------

local socket = checked_require("socket")
local socket_require = require("socket")

assert(socket == socket_require)
```

The type-hint of `require()` could then be changed to the following:

```lua
---@generic T : string
---@param module_name T
---@return Require module
function require(module_name) end
```

The language server already has a way to make global functions behave like `require` built-in, in the form of the `"Lua.runtime.special"` setting. This type would essentially do the same, except that it would be more powerful / broadly usable, since it could be applied to any variable. It would also be easier to use, since it's just another type in your code instead of something hiding in a config file.

Start by tracing how the language server handles require() type hints and the Lua.runtime.special setting. Define what Require should do for literal module names, wrappers, and the shown checked_require example; done means the wrapper and direct require resolve to the same module type.

Written by the indexing model from the issue text.