Support for keyring in runtimes (#2044)

This functionality is required for #1984.

This PR enables
[`sp-keyring`](https://github.com/paritytech/polkadot-sdk/blob/21d36b7b4229c4d5225944f197918cde23fda4ea/substrate/primitives/keyring/src/sr25519.rs#L31-L40)
in `no-std` environments, allowing to generate the public key (e.g.
`AccountKeyring::Alice.public().to_ss58check()`), which can be later
used in the any of built-in [_runtime-genesis-config_
variant](https://github.com/paritytech/polkadot-sdk/blob/21d36b7b4229c4d5225944f197918cde23fda4ea/polkadot/node/service/src/chain_spec.rs#L1066-L1073).


The proposal is as follows:
- expose [`core::Pair`
trait](https://github.com/paritytech/polkadot-sdk/blob/d6f15306282e3de848a09c9aa9cba6f95a7811f0/substrate/primitives/core/src/crypto.rs#L832)
in `no-std`,
- `full_crypto` feature enables `sign` method,
- `std` feature enables `generate_with_phrase` and `generate` methods
(randomness is required),
- All other functionality, currently gated by `full_crypto` will be
available unconditionally (`no-std`):
-- `from_string`
-- `from_string_with_seed`
-- `from seed`
-- `from_seed_slice`
-- `from_phrase`
-- `derive`
-- `verify`

---

Depends on https://github.com/rust-bitcoin/rust-bip39/pull/57

---------

Co-authored-by: command-bot <>
Co-authored-by: Davide Galassi <davxy@datawok.net>

substrate/primitives/application-crypto/src/traits.rs

@@ -18,9 +18,7 @@
 use codec::Codec;
 use scale_info::TypeInfo;
 
-#[cfg(feature = "full_crypto")]
-use sp_core::crypto::Pair;
-use sp_core::crypto::{CryptoType, CryptoTypeId, IsWrappedBy, KeyTypeId, Public};
+use sp_core::crypto::{CryptoType, CryptoTypeId, IsWrappedBy, KeyTypeId, Pair, Public};
 use sp_std::{fmt::Debug, vec::Vec};
 
 /// Application-specific cryptographic object.
@@ -45,24 +43,14 @@ pub trait AppCrypto: 'static + Sized + CryptoType {
 	type Signature: AppSignature;
 
 	/// The corresponding key pair type in this application scheme.
-	#[cfg(feature = "full_crypto")]
 	type Pair: AppPair;
 }
 
 /// Type which implements Hash in std, not when no-std (std variant).
-#[cfg(any(feature = "std", feature = "full_crypto"))]
 pub trait MaybeHash: sp_std::hash::Hash {}
-#[cfg(any(feature = "std", feature = "full_crypto"))]
 impl<T: sp_std::hash::Hash> MaybeHash for T {}
 
-/// Type which implements Hash in std, not when no-std (no-std variant).
-#[cfg(all(not(feature = "std"), not(feature = "full_crypto")))]
-pub trait MaybeHash {}
-#[cfg(all(not(feature = "std"), not(feature = "full_crypto")))]
-impl<T> MaybeHash for T {}
-
 /// Application-specific key pair.
-#[cfg(feature = "full_crypto")]
 pub trait AppPair:
 	AppCrypto + Pair<Public = <Self as AppCrypto>::Public, Signature = <Self as AppCrypto>::Signature>
 {