Feature request: Quick Fix for adding function

One feature I miss from a previous life in Eclipse/Java is the ability to quick fix an "is undefined or private" error by adding the function at the end of the correct module. For example, if I am writing code and come across the need to get all users for a particular country, but that doesn't currently exist in the Accounts context, I might write:

```elixir
assign(socket, :users_in_country, Accounts.get_all_users_for_country(country))
```

and then ElixirLS would complain that `MyApp.Accounts.get_all_users_for_country/1 is undefined or private`.

The quick fix would insert the following to the end of the `MyApp.Accounts` module and jump over to that file:

```elixir
def get_all_users_for_country(country) do

end
end
```
with the cursor inside the function, ready to implement it.