fuzz: Shuffle files before testing them

When iterating over all fuzz input files in a folder, the order should
not matter.

However, shuffling may be useful to detect non-determinism.

Thus, shuffle in fuzz.cpp, when using neither libFuzzer, nor AFL.

Also, shuffle in the deterministic-fuzz-coverage tool, when using
libFuzzer.

contrib/devtools/deterministic-fuzz-coverage/src/main.rs

@@ -133,7 +133,7 @@ fn deterministic_coverage(
             let output = {
                 let mut cmd = Command::new(fuzz_exe);
                 if using_libfuzzer {
-                    cmd.arg("-runs=1");
+                    cmd.args(["-runs=1", "-shuffle=1", "-prefer_small=0"]);
                 }
                 cmd
             }