AK+Everywhere: Change AK::fill_with_random to accept a Bytes object

Rather than the very C-like API we currently have, accepting a void* and
a length, let's take a Bytes object instead. In almost all existing
cases, the compiler figures out the length.

Userland/Libraries/LibCrypto/Curves/Ed25519.cpp

@@ -19,7 +19,7 @@ ErrorOr<ByteBuffer> Ed25519::generate_private_key()
     // about randomness.
 
     auto buffer = TRY(ByteBuffer::create_uninitialized(key_size()));
-    fill_with_random(buffer.data(), buffer.size());
+    fill_with_random(buffer);
     return buffer;
 };