Export GRANDPA AuthorityPair when full_crypto is enabled (#4872)

* Export crypto_full feature in primitives/finality-grandpa

* Export GRANDPA AuthorityPair when full_crypto is enabled

substrate/primitives/finality-grandpa/Cargo.toml

@@ -23,3 +23,6 @@ std = [
 	"sp-api/std",
 	"sp-runtime/std",
 ]
+full_crypto = [
+	"app-crypto/full_crypto"
+]

substrate/primitives/finality-grandpa/src/lib.rs

@@ -34,7 +34,7 @@ mod app {
 }
 
 /// The grandpa crypto scheme defined via the keypair type.
-#[cfg(feature = "std")]
+#[cfg(any(feature = "std", feature = "full_crypto"))]
 pub type AuthorityPair = app::Pair;
 
 /// Identity of a Grandpa authority.