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.

Demos/DynamicObject/main.cpp

@@ -39,12 +39,8 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-int main(int argc, char** argv, char** env)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv, [[maybe_unused]] char** env)
 {
-    (void)argc;
-    (void)argv;
-    (void)env;
-
     printf("Well Hello Friends!\n");
     printf("trying to open /etc/fstab for writing..\n");
     int rc = open("/etc/fstab", O_RDWR);