SignerSource: rename input scheme to prompt, default to bip44 solana base key (#17154) (#17159)

* Rename ask to prompt

* Default to Solana bip44 base if no derivation-path

* Add SignerSource legacy field, support legacy ASK

* Update docs

* Fix docs: validator current doesn't support uri SignerSources

(cherry picked from commit a5ec3a0547)

Co-authored-by: Tyera Eulberg <teulberg@gmail.com>

sdk/src/signature.rs

@@ -398,16 +398,13 @@ pub fn keypair_from_seed(seed: &[u8]) -> Result<Keypair, Box<dyn error::Error>>
 }
 
 /// Generates a Keypair using Bip32 Hierarchical Derivation if derivation-path is provided;
-/// otherwise builds standard Keypair using the seed as SecretKey
+/// otherwise generates the base Bip44 Solana keypair from the seed
 pub fn keypair_from_seed_and_derivation_path(
     seed: &[u8],
     derivation_path: Option<DerivationPath>,
 ) -> Result<Keypair, Box<dyn error::Error>> {
-    if let Some(derivation_path) = derivation_path {
-        bip32_derived_keypair(seed, derivation_path).map_err(|err| err.to_string().into())
-    } else {
-        keypair_from_seed(seed)
-    }
+    let derivation_path = derivation_path.unwrap_or_else(DerivationPath::default);
+    bip32_derived_keypair(seed, derivation_path).map_err(|err| err.to_string().into())
 }
 
 /// Generates a Keypair using Bip32 Hierarchical Derivation