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/bin/node-template/runtime/src/lib.rs

@@ -315,6 +315,10 @@ impl_runtime_apis! {
 			Executive::apply_extrinsic(extrinsic)
 		}
 
+		fn apply_trusted_extrinsic(extrinsic: <Block as BlockT>::Extrinsic) -> ApplyExtrinsicResult {
+			Executive::apply_trusted_extrinsic(extrinsic)
+		}
+
 		fn finalize_block() -> <Block as BlockT>::Header {
 			Executive::finalize_block()
 		}