Refactor sr-api to not depend on client anymore (#4086)

* Refactor sr-api to not depend on client anymore

* Fix benches

* Apply suggestions from code review

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Apply suggestions from code review

substrate/core/block-builder/runtime-api/src/lib.rs

@@ -0,0 +1,43 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! The block builder runtime api.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use sr_primitives::{traits::Block as BlockT, ApplyResult};
+
+use inherents::{InherentData, CheckInherentsResult};
+
+sr_api::decl_runtime_apis! {
+	/// The `BlockBuilder` api trait that provides the required functionality for building a block.
+	#[api_version(3)]
+	pub trait BlockBuilder {
+		/// Apply the given extrinsics.
+		fn apply_extrinsic(extrinsic: <Block as BlockT>::Extrinsic) -> ApplyResult;
+		/// Finish the current block.
+		#[renamed("finalise_block", 3)]
+		fn finalize_block() -> <Block as BlockT>::Header;
+		/// Generate inherent extrinsics. The inherent data will vary from chain to chain.
+		fn inherent_extrinsics(
+			inherent: InherentData,
+		) -> rstd::vec::Vec<<Block as BlockT>::Extrinsic>;
+		/// Check that the inherents are valid. The inherent data will vary from chain to chain.
+		fn check_inherents(block: Block, data: InherentData) -> CheckInherentsResult;
+		/// Generate a random seed.
+		fn random_seed() -> <Block as BlockT>::Hash;
+	}
+}