Add UnnecessaryAliasExpansion check

[remi]

I noticed we don’t have a check for this kind of code :

alias Foo.{Bar}

Alias expansion with braces is great but I think it affects the code readability when it’s used with a list containing a single item; it should be written :

alias Foo.Bar

This new UnnecessaryAliasExpansion check makes sure this rule is followed 😄

[rrrene]

@remiprev Nice work 👍 Thx!