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/LibC/assert.h

@@ -41,7 +41,7 @@ __attribute__((noreturn)) void __assertion_failed(const char* msg);
         } while (0)
 #    define ASSERT_NOT_REACHED() assert(false)
 #else
-#    define assert(expr) ((void)0)
+#    define assert(expr) (void(0))
 #    define ASSERT_NOT_REACHED() CRASH()
 #endif