Merge #19215: psbt: Include and allow both non_witness_utxo and witness_utxo for segwit inputs

84d295e513 tests: Check that segwit inputs in psbt have both UTXO types (Andrew Chow)
4600479058 psbt: always put a non_witness_utxo and don't remove it (Andrew Chow)
5279d8bc07 psbt: Allow both non_witness_utxo and witness_utxo (Andrew Chow)
72f6bec1da rpc: show both UTXOs in decodepsbt (Andrew Chow)

Pull request description:

  Due to recent changes to hardware wallets, the full previous transaction will need to be provided for segwit inputs. Since some software may be checking for the existence of a `witness_utxo` to determine whether to produce a segwit signature, we keep that field to ease the transition.

  Because all of the sanity checks implemented by the `IsSane` functions were related to having mixed segwit and non-segwit data in a PSBT, those functions are removed as those checks are no longer proper.

  Some tests are updated/removed to accommodate this and a simple test added to check that both UTXOs are being added to segwit inputs.

  As discussed in the wallet IRC meeting, our own signer will not require `non_witness_utxo` for segwit inputs.

ACKs for top commit:
  Sjors:
    utACK 84d295e513 (didn't retest compared to 836d6fc, but fortunately HWI's CI tracks our master branch, with a bunch of hardware wallet simulators)
  ryanofsky:
    Code review re-ACK 84d295e513. No changes since last review, but now I understand the context better. I think it would good to improve the comments as suggested https://github.com/bitcoin/bitcoin/pull/19215#discussion_r447889473 and maybe refer to
  meshcollider:
    utACK 84d295e513

Tree-SHA512: ccc1fd3c16ac3859f5aca4fa489bd40f68be0b81bbdc4dd51188bbf28827a8642dc8b605a37318e5f16cf40f1c4910052dace2f27eca21bb58435f02a443e940

test/functional/rpc_psbt.py

@@ -38,6 +38,7 @@ class PSBTTest(BitcoinTestFramework):
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
 
+    # TODO: Re-enable this test with segwit v1
     def test_utxo_conversion(self):
         mining_node = self.nodes[2]
         offline_node = self.nodes[0]
@@ -156,6 +157,10 @@ class PSBTTest(BitcoinTestFramework):
         # spend single key from node 1
         rawtx = self.nodes[1].walletcreatefundedpsbt([{"txid":txid,"vout":p2wpkh_pos},{"txid":txid,"vout":p2sh_p2wpkh_pos},{"txid":txid,"vout":p2pkh_pos}], {self.nodes[1].getnewaddress():29.99})['psbt']
         walletprocesspsbt_out = self.nodes[1].walletprocesspsbt(rawtx)
+        # Make sure it has both types of UTXOs
+        decoded = self.nodes[1].decodepsbt(walletprocesspsbt_out['psbt'])
+        assert 'non_witness_utxo' in decoded['inputs'][0]
+        assert 'witness_utxo' in decoded['inputs'][0]
         assert_equal(walletprocesspsbt_out['complete'], True)
         self.nodes[1].sendrawtransaction(self.nodes[1].finalizepsbt(walletprocesspsbt_out['psbt'])['hex'])
 
@@ -352,7 +357,8 @@ class PSBTTest(BitcoinTestFramework):
         for i, signer in enumerate(signers):
             self.nodes[2].unloadwallet("wallet{}".format(i))
 
-        self.test_utxo_conversion()
+        # TODO: Re-enable this for segwit v1
+        # self.test_utxo_conversion()
 
         # Test that psbts with p2pkh outputs are created properly
         p2pkh = self.nodes[0].getnewaddress(address_type='legacy')