Add (for_expression) to locals.scm

[rwjblue]

This change does two main things:

1. Indicate that (for_expression)'s introduce a @local.scope (this is the scope for the enumerators to be used within the loop).
2. Indicate that the (identifiers) within the (enumerators) are @local.definitions.

---

For the following example snippet:

val fruits = List("apple", "banana", "avocado", "papaya")

val countsToFruits = fruits.groupBy(fruit => fruit.count(_ == 'a'))

for ((count, fruits) <- countsToFruits) {
  println(s"with (fruits) 'a' × $count = $fruits")
}

The count and fruits identifiers are new definitions introduced by the for expressions scope.

[ckipp01]

Hey @rwjblue, same comment as the other PR. Would you be willing to add in some tests in the highlight queries showing this?