CLI: dynamic signing reboot (#8384)

* Add keypair_util_from_path helper

* Cli: impl config.keypair as a trait object

* SDK: Add Debug and PartialEq for dyn Signer

* ClapUtils: Arg parsing from pubkey+signers to Presigner

* Impl Signers for &dyn Signer collections

* CLI: Add helper for getting signers from args

* CLI: Replace SigningAuthority with Signer trait-objs

* CLI: Drop disused signers command field

* CLI: Drop redundant tests

* Add clap validator that handles all current signer types

* clap_utils: Factor Presigner resolution to helper

* SDK: `From` for boxing Signer implementors to trait objects

* SDK: Derive `Clone` for `Presigner`

* Remove panic

* Cli: dedup signers in transfer for remote-wallet ergonomics

* Update docs vis-a-vis ASK changes

* Cli: update transaction types to use new dynamic-signer methods

* CLI: Fix tests No. 1

what to do about write_keypair outstanding

* Work around `CliConfig`'s signer not necessarily being a `Keypair`

* CLI: Fix tests No. 2

* Remove unused arg

* Remove unused methods

* Move offline arg constants upstream

* Make cli signing fallible

Co-authored-by: Trent Nelson <trent.a.b.nelson@gmail.com>

clap-utils/src/input_parsers.rs

@@ -1,4 +1,6 @@
-use crate::keypair::{keypair_from_seed_phrase, ASK_KEYWORD, SKIP_SEED_PHRASE_VALIDATION_ARG};
+use crate::keypair::{
+    keypair_from_seed_phrase, keypair_util_from_path, ASK_KEYWORD, SKIP_SEED_PHRASE_VALIDATION_ARG,
+};
 use chrono::DateTime;
 use clap::ArgMatches;
 use solana_remote_wallet::remote_wallet::DerivationPath;
@@ -93,6 +95,18 @@ pub fn pubkeys_sigs_of(matches: &ArgMatches<'_>, name: &str) -> Option<Vec<(Pubk
     })
 }
 
+// Return a signer from matches at `name`
+pub fn signer_of(
+    name: &str,
+    matches: &ArgMatches<'_>,
+) -> Result<Option<Box<dyn Signer>>, Box<dyn std::error::Error>> {
+    if let Some(location) = matches.value_of(name) {
+        keypair_util_from_path(matches, location, name).map(Some)
+    } else {
+        Ok(None)
+    }
+}
+
 pub fn lamports_of_sol(matches: &ArgMatches<'_>, name: &str) -> Option<u64> {
     value_of(matches, name).map(sol_to_lamports)
 }