Two Rule Suggestions: multiple returns in function calls / table definitions and string concatenation

Nadie ha tomado este issue todavía.

### multiple returns in function calls / table definitions

```lua
local a = { "one", "two", "three" }
local b = { unpack(a), "four" }
local c = { "four", unpack(a) }
print(#b) -- 2
print(#c) -- 4
```
`unpack`'s behavior is quite unintuitive; when the output is not in the last position of a table definition, only the first element is actually included in the new table. (In fact, this not only applies to `unpack`, but to every function that returns multiple values – only happens most often with `unpack` that will people will notice, I assume.)

see explainer in the docs: https://www.lua.org/manual/5.3/manual.html#3.4

I think a diagnostic that reminds one of such cases would be very useful, since it's a common gotcha in lua.

## string concatenation

```lua
print("foo" + "bar")
```
Common mistake to not use `..` for string concatenation. Even though I am used to lua, it still happens to me all the time after coming back from writing in a different language. A diagnostic here would be useful. (And I am actually a bit surprised that there isn't one yet.)

Comienza con la sección del manual de Lua 5.3 enlazada en el issue, especialmente con las reglas de múltiples valores de retorno ilustradas mediante los ejemplos de tablas. Después, localiza los puntos de entrada de diagnóstico del language server para expresiones con múltiples valores de retorno en definiciones de tablas y para usar + con cadenas. Se considera terminado cuando ambos ejemplos producen diagnósticos útiles sin marcar incorrectamente código Lua válido.

Escrito por el modelo de indexación a partir del texto del issue.