accounts, eth, clique, signer: support for external signer API (#18079)
* accounts, eth, clique: implement external backend + move sighash calc to backend
* signer: implement account_Version on external API
* accounts/external: enable ipc, add copyright
* accounts, internal, signer: formatting
* node: go fmt
* flags: disallow --dev in combo with --externalsigner
* accounts: remove clique-specific signing method, replace with more generic
* accounts, consensus: formatting + fix error in tests
* signer/core: remove (test-) import cycle
* clique: remove unused import
* accounts: remove CliqueHash and avoid dependency on package crypto
* consensus/clique: unduplicate header encoding
43e8efe895