Build block without checking signatures (#4916)

* in executive

* in other places

* to UnsafeResult

* move doc comment

* apply suggestions

* allow validity mocking for TestXt

* add test

* augment checkable instead of another trait

* fix im online test

* blockbuilder dihotomy

* review suggestions

* update test

* Update client/block-builder/src/lib.rs

* updae spec_version

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/block-builder/src/lib.rs

@@ -121,11 +121,23 @@ where
 			backend,
 		})
 	}
+	
+	/// Push onto the block's list of extrinsics.
+	///
+	/// This will ensure the extrinsic can be validly executed (by executing it).
+	pub fn push(&mut self, xt: <Block as BlockT>::Extrinsic) -> Result<(), ApiErrorFor<A, Block>> {
+		self.push_internal(xt, false)
+	}
 
 	/// Push onto the block's list of extrinsics.
 	///
-	/// This will ensure the extrinsic can be validly executed (by executing it);
-	pub fn push(&mut self, xt: <Block as BlockT>::Extrinsic) -> Result<(), ApiErrorFor<A, Block>> {
+	/// This will treat incoming extrinsic `xt` as untrusted and perform additional checks
+	/// (currenty checking signature).
+	pub fn push_trusted(&mut self, xt: <Block as BlockT>::Extrinsic) -> Result<(), ApiErrorFor<A, Block>> {
+		self.push_internal(xt, true)
+	}
+
+	fn push_internal(&mut self, xt: <Block as BlockT>::Extrinsic, skip_signature: bool) -> Result<(), ApiErrorFor<A, Block>> {
 		let block_id = &self.block_id;
 		let extrinsics = &mut self.extrinsics;
 
@@ -152,12 +164,29 @@ where
 				}
 			})
 		} else {
-			self.api.map_api_result(|api| {
-				match api.apply_extrinsic_with_context(
+			let use_trusted = skip_signature && self
+				.api
+				.has_api_with::<dyn BlockBuilderApi<Block, Error = ApiErrorFor<A, Block>>, _>(
 					block_id,
-					ExecutionContext::BlockConstruction,
-					xt.clone(),
-				)? {
+					|version| version >= 5,
+				)?;
+
+			self.api.map_api_result(|api| {
+				let apply_result = if use_trusted {
+					api.apply_trusted_extrinsic_with_context(
+						block_id,
+						ExecutionContext::BlockConstruction,
+						xt.clone(),
+					)?
+				} else  { 
+					api.apply_extrinsic_with_context(
+						block_id,
+						ExecutionContext::BlockConstruction,
+						xt.clone(),
+					)?
+				};
+
+				match apply_result {
 					Ok(_) => {
 						extrinsics.push(xt);
 						Ok(())