Move parachain inherent data into its own crate (#326)

This renames and moves the `SystemInherentData` into its own crate.
The struct is now called `ParachainInherentData`. Besides moving the
struct, this also moves the code for creating this struct into this crate.

test/client/src/block_builder.rs

@@ -15,11 +15,10 @@
 // along with Cumulus.  If not, see <http://www.gnu.org/licenses/>.
 
 use crate::{Backend, Client};
-use cumulus_primitives_core::{
-	inherents::{SystemInherentData, SYSTEM_INHERENT_IDENTIFIER}, PersistedValidationData,
-};
-use cumulus_test_runtime::{Block, GetLastTimestamp};
+use cumulus_primitives_core::PersistedValidationData;
+use cumulus_primitives_parachain_inherent::{ParachainInherentData, INHERENT_IDENTIFIER};
 use cumulus_test_relay_sproof_builder::RelayStateSproofBuilder;
+use cumulus_test_runtime::{Block, GetLastTimestamp};
 use polkadot_primitives::v1::BlockNumber as PBlockNumber;
 use sc_block_builder::{BlockBuilder, BlockBuilderProvider};
 use sp_api::ProvideRuntimeApi;
@@ -101,8 +100,8 @@ impl InitBlockBuilder for Client {
 
 		inherent_data
 			.put_data(
-				SYSTEM_INHERENT_IDENTIFIER,
-				&SystemInherentData {
+				INHERENT_IDENTIFIER,
+				&ParachainInherentData {
 					validation_data,
 					relay_chain_state,
 					downward_messages: Default::default(),