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Ava Chow 76a33be21d Merge bitcoin/bitcoin#28307 : rpc, wallet: fix incorrect segwit redeem script size limit

2451a217dd test: addmultisigaddress, coverage for script size limits (furszy)
53302a0981 bugfix: addmultisigaddress, add unsupported operation for redeem scripts over 520 bytes (furszy)
9be6065cc0 test: coverage for 16-20 segwit multisig scripts (furszy)
9d9a91c4ea rpc: bugfix, incorrect segwit redeem script size used in signrawtransactionwithkey (furszy)
0c9fedfc45 fix incorrect multisig redeem script size limit for segwit (furszy)
f7a173b578 test: rpc_createmultisig, decouple 'test_sortedmulti_descriptors_bip67' (furszy)
4f33dbd8f8 test: rpc_createmultisig, decouple 'test_mixing_uncompressed_and_compressed_keys' (furszy)
25a81705d3 test: rpc_createmultisig, remove unnecessary checkbalances() (furszy)
b5a3289433 test: refactor, multiple cleanups in rpc_createmultisig.py (furszy)
3635d43268 test: rpc_createmultisig, remove manual wallet initialization (furszy)

Pull request description:

  Fixing https://github.com/bitcoin/bitcoin/issues/28250#issuecomment-1674830104 and more.

  Currently, redeem scripts longer than 520 bytes, which are technically valid under segwit rules, have flaws in the following processes:
  1) The multisig creation process fails to deduce the output descriptor, resulting in the generation of an incorrect descriptor. Additionally, the accompanying user warning is also inaccurate.
  2) The `signrawtransactionwithkey` RPC command fail to sign them.
  3) The legacy wallet `addmultisigaddress` wrongly discards them.

  The issue arises because most of these flows are utilizing the legacy spkm keystore, which imposes
  the [p2sh max redeem script size rule](ded6873340/src/script/signingprovider.cpp (L160)) on all scripts. Which blocks segwit redeem scripts longer than
  the max element size in all the previously mentioned processes (`createmultisig`, `addmultisigaddress`, and
  `signrawtransactionwithkey`).

  This PR fixes the problem, enabling the creation of multisig output descriptors involving more than 15 keys and
  allowing the signing of these scripts, along with other post-segwit redeem scripts that surpass the 520-byte
  p2sh limit.

  Important note:
  Instead of adding support for these longer redeem scripts in the legacy wallet, an "unsupported operation"
  error has been added. The reasons behind this decision are:

  1) The introduction of this feature brings about a compatibility-breaking change that requires downgrade
      protection; older wallets would be unable to interact with these "new" legacy wallets.

  2) Considering the ongoing deprecation of the legacy spkm, this issue provides another compelling
      reason to transition towards descriptors.

  Testing notes:
  To easily verify each of the fixes, I decoupled the tests into standalone commits. So they can be
  cherry-picked on top of master. Where `rpc_createmultisig.py` (with and without the `--legacy-wallet`
  arg) will fail without the bugs fixes commits.

  Extra note:
  The initial commits improves the `rpc_createmultisig.py` test in many ways. I found this test very
  antiquated, screaming for an update and cleanup.

ACKs for top commit:
  pinheadmz:
    ACK 2451a217dd
  theStack:
    Code-review ACK 2451a217dd
  achow101:
    ACK 2451a217dd

Tree-SHA512: 71794533cbd46b3a1079fb4e9d190d3ea3b615de0cbfa443466e14f05e4616ca90e12ce2bf07113515ea8113e64a560ad572bb9ea9d4835b6fb67b6ae596167f