Make for of loops require given object to be iterable

Switching to required is an optimization that should not have
adverse effects, because mutators should still allow us to
generate the same code without the performance impact of
throwing away as many generated programs.

Bug: 40272934
Change-Id: I636a6d22e80d18aab038eebbb041c26c92c9b3ac
Reviewed-on: https://chrome-internal-review.googlesource.com/c/v8/fuzzilli/+/8543122
Auto-Submit: Hendrik Wüthrich <whendrik@google.com>
Reviewed-by: Hendrik Wüthrich <whendrik@google.com>
Commit-Queue: Hendrik Wüthrich <whendrik@google.com>
Reviewed-by: Matthias Liedtke <mliedtke@google.com>

Author: whendrik-cmd

Sources/Fuzzilli/CodeGen/CodeGenerators.swift

@@ -1556,7 +1556,7 @@ public let CodeGenerators: [CodeGenerator] = [
         }
     },
 
-    RecursiveCodeGenerator("ForOfLoopGenerator", inputs: .preferred(.iterable)) { b, obj in
+    RecursiveCodeGenerator("ForOfLoopGenerator", inputs: .required(.iterable)) { b, obj in
         b.buildForOfLoop(obj) { _ in
             b.buildRecursive()
         }