break sp-api dependency cycle (#4352)

* move benches into tests, ignore non-passing doctests

* Rename sr-api folder

* Move test-primitives to primitives, use that for sp-api doctests

substrate/primitives/api/test/tests/ui/declaring_old_block.rs

@@ -0,0 +1,9 @@
+use sp_runtime::traits::Block as BlockT;
+
+sp_api::decl_runtime_apis! {
+	pub trait Api<Block: BlockT> {
+		fn test();
+	}
+}
+
+fn main() {}