Merge bitcoin/bitcoin#27884: test: Use TestNode datadir_path or chain_path where possible

aaaa3aefbd test: Use TestNode *_path properties where possible (MarcoFalke)
dddd89962b test: Allow pathlib.Path as RPC argument via authproxy (MarcoFalke)
fa41614a0a scripted-diff: Use wallets_path and chain_path where possible (MarcoFalke)
fa493fadfb test: Use wallet_dir lambda in wallet_multiwallet test where possible (MarcoFalke)

Pull request description:

  It seems inconsistent, fragile and verbose to:

  * Call `get_datadir_path` to recreate the path that already exists as field in TestNode
  * Call `os.path.join` with the hardcoded chain name or `self.chain` to recreate the TestNode `chain_path` property
  * Sometimes even use the hardcoded node dir name (`"node0"`)

  Fix all issues by using the TestNode properties.

ACKs for top commit:
  willcl-ark:
    re-ACK aaaa3aefbd
  theStack:
    Code-review ACK aaaa3aefbd 🌊

Tree-SHA512: e4720278085beb8164e1fe6c1aa18f601558a9263494ce69a83764c1487007de63ebb51d1b1151862dc4d5b49ded6162a5c1553cd30ea1c28627d447db4d8e72

test/functional/rpc_createmultisig.py

@@ -157,7 +157,7 @@ class RpcCreateMultiSigTest(BitcoinTestFramework):
                 try:
                     node1.loadwallet('wmulti')
                 except JSONRPCException as e:
-                    path = os.path.join(self.options.tmpdir, "node1", "regtest", "wallets", "wmulti")
+                    path = self.nodes[1].wallets_path / "wmulti"
                     if e.error['code'] == -18 and "Wallet file verification failed. Failed to load database path '{}'. Path does not exist.".format(path) in e.error['message']:
                         node1.createwallet(wallet_name='wmulti', disable_private_keys=True)
                     else: