Merge #15749: Fix: importmulti only imports origin info for PKH outputs

b5d398772 Take non-importing keys into account for spendability warning in descriptor import (Pieter Wuille)
6e597001a Import all origin info in importmulti; even for non-importing pubkeys (Pieter Wuille)
9a93c91c8 Keep full pubkeys in FlatSigningProvider::origins (Pieter Wuille)

Pull request description:

  This fixes #15743 and #15742.

  Since #15263, pubkeys are no longer imported for non-PKH (or WPKH, or any wrapped form of those) outputs, as that would incorrectly mark outputs to single-key versions of multisig policies as watched.

  As a side effect, this change also caused origin info not to be imported anymore for multisig policies.

  Fix this by plumbing through the full pubkey information for origins in FlatSigningProvider, and then importing all origin info we have in `importmulti` (knowing more never hurts, and additional origin information has no negative consequences like importing the pubkeys themselves).

ACKs for commit b5d398:
  MeshCollider:
    utACK b5d3987724

Tree-SHA512: 37caa2be8d01b8baa12f70a58eaa7c583f5f0afbe012e02936dd8790dc5dc852f880b77258b34ddb68cae30c029585f2d1c4f5d00015380557a1e8b471e500f3

test/functional/wallet_importmulti.py

@@ -629,7 +629,8 @@ class ImportMultiTest(BitcoinTestFramework):
         self.log.info("Should import a 1-of-2 bare multisig from descriptor")
         self.test_importmulti({"desc": descsum_create("multi(1," + key1.pubkey + "," + key2.pubkey + ")"),
                                "timestamp": "now"},
-                              success=True)
+                              success=True,
+                              warnings=["Some private keys are missing, outputs will be considered watchonly. If this is intentional, specify the watchonly flag."])
         self.log.info("Should not treat individual keys from the imported bare multisig as watchonly")
         test_address(self.nodes[1],
                      key1.p2pkh_addr,