`GetFormatSpecifierLocationsAndArity` returns duplicated entries in computation expressions

[auduchinok]

Consider this case:

seq {
    sprintf "%d" 1
}

Calling GetFormatSpecifierLocationsAndArity on check file results will return duplicated entries for %s.

This could be happening due to some tree rewriting during computation expressions analysis. It also means that some analysis may be duplicated, worsening performance.