Keystore overhaul (final) (#13683)

* Introduce keystore specialized sign methods

* Get rid of 'AppKey::UntypedGeneric' associated type.

Untyped generics are accessible using associated types 'Generic' associated type.
I.e. <T as AppKey>::Public::Generic

* Get rid of 'CryptoTypePublicPair'

* Trivial fix

* Small refactory of local keystore implementations

* Remove 'crypto_id' method from 'Public'

* Trivial rename of 'AppKey' to 'AppCrypto'

* Remove unused import

* Improve docs

* Better signature related errors for authority-discovery

* Apply review suggestion

* Apply review suggestions

Co-authored-by: Koute <koute@users.noreply.github.com>

* Authority discoverty signing error revisited

* Signing error revisited for babe and aura as well

* Further cleanup

---------

Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/primitives/consensus/common/src/error.rs

@@ -48,8 +48,8 @@ pub enum Error {
 	#[error("Chain lookup failed: {0}")]
 	ChainLookup(String),
 	/// Signing failed.
-	#[error("Failed to sign using key: {0:?}. Reason: {1}")]
-	CannotSign(Vec<u8>, String),
+	#[error("Failed to sign: {0}")]
+	CannotSign(String),
 	/// Some other error.
 	#[error(transparent)]
 	Other(#[from] Box<dyn std::error::Error + Sync + Send + 'static>),