Unnecessary variables generated for string literals as partial function args

[cknitt]

This is a regression in current master that is similar to the already solved #5454.

Consider the following ReScript code:

let concat = (a, b, c) => a ++ b ++ c

let result = ["a", "b"]->Js.Array2.map(concat("c", "d"))

In ReScript 9, this compiles to:

function concat(a, b, c) {
  return a + b + c;
}

var result = [
    "a",
    "b"
  ].map(function (param) {
      return concat("c", "d", param);
    });

In current master, this compiles to

function concat(a, b, c) {
  return a + b + c;
}

var partial_arg = "d";

var partial_arg$1 = "c";

var result = [
    "a",
    "b"
  ].map(function (param) {
      return concat(partial_arg$1, partial_arg, param);
    });

[cknitt]

Like with #5454, the same behavior can be reproduced in ReScript 9.1.4 if using backtick strings instead of double quoted strings, i.e.:

let result = ["a", "b"]->Js.Array2.map(concat(`c`, `d`))

[cristianoc]

This seems unrelated to being literals.

let concat = (a, b, c) => a + b + c

let result = (a,b,c,d) => [a, b]->Js.Array2.map(concat(c, d))

let concat2 = (a, b, c) => a ++ b ++ c

let result2 = ["a", "b"]->Js.Array2.map(concat2("c", "d"))

gives

function concat(a, b, c) {
  return (a + b | 0) + c | 0;
}

function result(a, b, c, d) {
  return [
            a,
            b
          ].map(function (param) {
              return concat(c, d, param);
            });
}

function concat2(a, b, c) {
  return a + b + c;
}

var partial_arg = "d";

var partial_arg$1 = "c";

var result2 = [
    "a",
    "b"
  ].map(function (param) {
      return concat2(partial_arg$1, partial_arg, param);
    });