Fix nostd build of several crates (#4060)

Preparation for https://github.com/paritytech/polkadot-sdk/pull/3935

Changes:
- Add some `default-features = false` for the case that a crate and that
dependency both support nostd builds.
- Shuffle files around of some benchmarking-only crates. These
conditionally disabled the `cfg_attr` for nostd and pulled in libstd.
Example [here](https://github.com/ggwpez/zepter/pull/95). The actual
logic is moved into a `inner.rs` to preserve nostd capability of the
crate in case the benchmarking feature is disabled.
- Add some `use sp_std::vec` where needed.
- Remove some `optional = true` in cases where it was not optional.
- Removed one superfluous `cfg_attr(not(feature = "std"), no_std..`.

All in all this should be logical no-op.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/atomic-swap/src/lib.rs

@@ -58,6 +58,7 @@ use frame_system::pallet_prelude::BlockNumberFor;
 use scale_info::TypeInfo;
 use sp_io::hashing::blake2_256;
 use sp_runtime::RuntimeDebug;
+use sp_std::vec::Vec;
 
 /// Pending atomic swap operation.
 #[derive(Clone, Eq, PartialEq, RuntimeDebugNoBound, Encode, Decode, TypeInfo, MaxEncodedLen)]