…chor

60ea1d8 [CI][Tests] Move sapling functional tests to their own list (random-zebra)
03aec32 [Tests] Add sapling_mempool to test_runner and re-sort the list (random-zebra)
c3a1fff [Test] Add sapling_mempool functional test (random-zebra)
101978d [RPC] Introduce getbestsaplinganchor to get the most recent sapling root (random-zebra)

Pull request description:

  Based on top of:
  - [x] #1958
  - [x] #1964

  This adds a functional test to check the bahavior of sapling transactions with the mempool.
  Specifically, it verifies the nullifiers/anchor management introduced in #1958:
  - If a transaction spends a sapling note, already spent by another in-mempool transaction, it's not accepted in the mempool.
  - Same if it tries to double-spend a note already spent on chain.
  - If, after disconnecting a block, the sapling merkle tree root changes, any transaction that spends a note referencing the old root must be evicted from the mempool.

  In order to verify the last point, a simple RPC `getbestsaplinganchor` is introduced in the "blockchain" category.
  It returns the `pcoinsTip` best anchor.

  Note: without 1958, the test crashes the node, as two transactions spending the same note can both enter the mempool, but then the assertions in the memory pool consistency checks fail during block creation.

ACKs for top commit:
  furszy:
    Pretty nice!, code review ACK 60ea1d8
  Fuzzbawls:
    utACK 60ea1d8

Tree-SHA512: c321d7866bec56fca31d48286ac28ae44f27c48232919fd3f66fcc858a558b17cc0580163790c74290f376049fa44391a1033eb582ff9716b502673f535048d6

467b0d8 [Tests] Check delegations with sapling transactions (random-zebra)
d412525 [RPC] Add fUseShielded parameter to delegatestake/rawdelegatestake (random-zebra)
847d278 [Trivial] Missing newline in delegatestake (random-zebra)
7440709 [Validation] Don't reject sapling txes with P2CS outputs (random-zebra)

Pull request description:

  Enable pay-to-cold-staking outputs in shielded transactions.
  Add the option in `delegatestake`/`rawdelegatestake` to spend shielded funds directly to P2CS (without having to unshield them first).

  Add functional test.

  Based on top of
  - [x] #1964
  - [x] #1967
  - [x] #1969

  Starts with `[Validation] Don't reject sapling txes with P2CS outputs` (461d4ea69ea21ea639ae639d4248b4ef28312429)

ACKs for top commit:
  furszy:
    Looking good, ACK 467b0d8
  Fuzzbawls:
    ACK 467b0d8

Tree-SHA512: 88752fe1550def605b90cc894d0666f5c37dd8f075566e976c8fbfaa6e088ee0c1bb028e1885411b739781fda6ebac12a5c99fc19a06f453e594441ee1e1b599