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

Personne n'a encore pris cette issue.

### 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.)

Commencez par la section du manuel de Lua 5.3 liée dans l’issue, en particulier par les règles des retours multiples illustrées par les exemples de tables. Localisez ensuite les points d’entrée des diagnostics du language server pour les expressions à retours multiples dans les définitions de tables et pour l’utilisation de + avec des chaînes. Le travail est terminé lorsque les deux exemples produisent des diagnostics utiles sans signaler à tort du code Lua valide.

Rédigé par le modèle d'indexation à partir du texte de l'issue.