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/core/src/lib.rs

@@ -46,7 +46,6 @@ pub use sp_debug_derive::RuntimeDebug;
 #[cfg(feature = "serde")]
 pub use impl_serde::serialize as bytes;
 
-#[cfg(feature = "full_crypto")]
 #[deprecated(
 	since = "27.0.0",
 	note = "`sp-crypto-hashing` re-exports will be removed after June 2024. Use `sp-crypto-hashing` instead."
@@ -58,7 +57,6 @@ pub mod crypto;
 pub mod hexdisplay;
 pub use paste;
 
-#[cfg(any(feature = "full_crypto", feature = "std"))]
 mod address_uri;
 #[cfg(feature = "bandersnatch-experimental")]
 pub mod bandersnatch;
@@ -87,7 +85,6 @@ pub use self::{
 	hash::{convert_hash, H160, H256, H512},
 	uint::{U256, U512},
 };
-#[cfg(feature = "full_crypto")]
 pub use crypto::{ByteArray, DeriveJunction, Pair, Public};
 
 #[cfg(feature = "std")]