LibWeb: Add the Web::Crypto namespace, built-in, and getRandomValues

Since we don't support IDL typedefs or unions yet, the responsibility
of verifying the type of the argument is temporarily moved from the
generated Wrapper to the implementation.

Userland/Libraries/LibWeb/Crypto/Crypto.idl

@@ -0,0 +1,7 @@
+[Exposed=(Window,Worker)]
+interface Crypto {
+  // TODO: [SecureContext] readonly attribute SubtleCrypto subtle;
+
+  // FIXME: the argument and the return value should be of type ArrayBufferView
+  any getRandomValues(any array);
+};