Proper conditional compile for dummy variant/function

[NingLin-P]

There is a lot of [cfg(any(feature = "std", feature = "runtime-benchmarks"))] in the codebase for dummy variants/functions that are only used for tests/benchmarks. Ideally, we should not use std but instead use #[cfg(any(test, feature = "runtime-benchmarks"))] but these items are used cross-crate and the crate is imported as production not test.

To handle them properly we need to add a new feature to the crate that contains these dummy variants/functions and add a new dependency with this feature under the [dev-dependencies] in all the crates that use it.