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/SECP256r1.cpp

@@ -357,7 +357,7 @@ static bool is_point_on_curve(JacobianPoint const& point)
 ErrorOr<ByteBuffer> SECP256r1::generate_private_key()
 {
     auto buffer = TRY(ByteBuffer::create_uninitialized(32));
-    fill_with_random(buffer.data(), buffer.size());
+    fill_with_random(buffer);
     return buffer;
 }