Everywhere: Switch from (void) to [[maybe_unused]] (#4473)

Problem:
- `(void)` simply casts the expression to void. This is understood to
  indicate that it is ignored, but this is really a compiler trick to
  get the compiler to not generate a warning.

Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.

Note:
- Functions taking a `(void)` argument list have also been changed to
  `()` because this is not needed and shows up in the same grep
  command.

Libraries/LibJS/Runtime/IteratorOperations.cpp

@@ -87,9 +87,8 @@ Object* iterator_next(Object& iterator, Value value)
     return &result.as_object();
 }
 
-void iterator_close(Object& iterator)
+void iterator_close([[maybe_unused]] Object& iterator)
 {
-    (void)iterator;
     TODO();
 }