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/Accessor.h

@@ -63,7 +63,7 @@ public:
         if (!m_setter)
             return;
         // FIXME: It might be nice if we had a way to communicate to our caller if an exception happened after this.
-        (void)vm().call(*m_setter, this_value, setter_value);
+        [[maybe_unused]] auto rc = vm().call(*m_setter, this_value, setter_value);
     }
 
     void visit_edges(Cell::Visitor& visitor) override