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.

Meta/Lagom/Fuzzers/FuzzRegexECMA262.cpp

@@ -32,7 +32,6 @@
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
     auto pattern = AK::StringView(static_cast<const unsigned char*>(data), size);
-    Regex<ECMA262> re(pattern);
-    (void)re;
+    [[maybe_unused]] auto re = Regex<ECMA262>(pattern);
     return 0;
 }