feat: compute pallet/storage prefix hash at compile time (#1539)

Since the hash rules of this part of the `pallet_prefix/storage_prefix`
are always fixed, we can put the runtime calculation into compile time.

---
polkadot address: 15ouFh2SHpGbHtDPsJ6cXQfes9Cx1gEFnJJsJVqPGzBSTudr

---------

Co-authored-by: Juan <juangirini@gmail.com>
Co-authored-by: command-bot <>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/support/procedural/src/pallet/parse/helper.rs

@@ -15,7 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use quote::ToTokens;
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
 use syn::spanned::Spanned;
 
 /// List of additional token to be used for parsing.
@@ -610,3 +611,16 @@ pub fn check_pallet_call_return_type(type_: &syn::Type) -> syn::Result<()> {
 
 	syn::parse2::<Checker>(type_.to_token_stream()).map(|_| ())
 }
+
+pub(crate) fn two128_str(s: &str) -> TokenStream {
+	bytes_to_array(sp_core_hashing::twox_128(s.as_bytes()).into_iter())
+}
+
+pub(crate) fn bytes_to_array(bytes: impl IntoIterator<Item = u8>) -> TokenStream {
+	let bytes = bytes.into_iter();
+
+	quote!(
+		[ #( #bytes ),* ]
+	)
+	.into()
+}