Hide benchmarks behind a feature flag (#5024)

* Hide benchmarks behind a feature flag

* Propage attributes in impl_runtime_apis macro

* Bump impl_version

* Fillter cfg attributes

* Hide more things under the feature

* Fix set_block_number availability

* Rename filter_attrs -> filter_cfg_attrs

* Rename runtime_benchmarks to runtime-benchmarks

substrate/frame/balances/src/lib.rs

@@ -155,6 +155,7 @@ mod tests_composite;
 #[cfg(test)]
 #[macro_use]
 mod tests;
+#[cfg(feature = "runtime-benchmarks")]
 mod benchmarking;
 
 use sp_std::prelude::*;