Remapping of operators to identifiers in n-ary calls

```
julia> JuliaSyntax.parse(JuliaSyntax.GreenNode, "a+b+c")
     1:5      │[call]
     1:1      │  Identifier             ✔
     2:2      │  Identifier             ✔
     3:3      │  Identifier             ✔
     4:4      │  +
     5:5      │  Identifier             ✔
```