Implement Bip32 for seed-phrase/passphrase signing (#16942)

* Add Keypair helpers for bip32 derivation

* Plumb bip32 for SignerSourceKind::Ask

* Support full-path querystring

* Use as_ref

* Add public wrappers for from_uri cases

* Support master root derivations (and fix too-deep print

* Add ask:// HD documentation

* Update ASK elsewhere in docs

docs/src/running-validator/validator-start.md

@@ -155,7 +155,7 @@ solana-keygen new --no-outfile
 The corresponding identity public key can now be viewed by running:
 
 ```bash
-solana-keygen pubkey ASK
+solana-keygen pubkey ask://
 ```
 
 and then entering your seed phrase.
@@ -294,8 +294,8 @@ The ledger will be placed in the `ledger/` directory by default, use the
 > [paper wallet seed phrase](../wallet-guide/paper-wallet.md)
 > for your `--identity` and/or
 > `--authorized-voter` keypairs. To use these, pass the respective argument as
-> `solana-validator --identity ASK ... --authorized-voter ASK ...` and you will be
-> prompted to enter your seed phrases and optional passphrase.
+> `solana-validator --identity ask:// ... --authorized-voter ask:// ...`
+> and you will be prompted to enter your seed phrases and optional passphrase.
 
 Confirm your validator connected to the network by opening a new terminal and
 running: