Merge bitcoin/bitcoin#32618: wallet: Remove ISMINE_WATCHONLY and watchonly from RPCs

b1a8ac07e9 doc: Release note for removed watchonly parameters and results (Ava Chow)
15710869e1 wallet: Remove ISMINE_WATCH_ONLY (Ava Chow)
4439bf4b41 wallet, spend: Remove fWatchOnly from CCoinControl (Ava Chow)
1337c72198 wallet, rpc: Remove watchonly from RPCs (Ava Chow)
e81d95d435 wallet: Remove watchonly balances (Ava Chow)
d20dc9c6aa wallet: Wallets without private keys cannot grind R (Ava Chow)
9991f49c38 test: Watchonly wallets should estimate larger size (Ava Chow)

Pull request description:

  Descriptor wallets do not use the watchonly behavior as it is not possible to mix watchonly and non-watchonly in a descriptor wallet. With legacy wallets now removed, all of the watchonly handling and reporting code is no longer needed. This PR removes watchonly options and results from the RPCs and the handling of watchonly things from the wallet's internals.

  With all of the watchonly things removed, ISMINE_WATCH_ONLY is removed as well.

  Split from #32523

  Depends on #32594 for tests that are easier to read

ACKs for top commit:
  Eunovo:
    ACK b1a8ac07e9
  maflcko:
    re-ACK b1a8ac07e9 🌈
  rkrux:
    ACK b1a8ac07e9
  furszy:
    light code review ACK b1a8ac07e9

Tree-SHA512: bc87f37a13294f7208991be8f93899b49e5bdf87c70e0f66d9c4cb09c03be6c202320406f27e9a35aa2f57319d19a3f0c07d5e5ddbc97c7edab165b1656d6612

doc/release-notes-32618.md

@@ -0,0 +1,7 @@
+Wallet
+------
+
+* Since descriptor wallets do not allow mixing watchonly and non-watchonly descriptors,
+the `include_watchonly` option (and its variants in naming) are removed from all RPCs
+that had it.
+* The `iswatchonly` field is removed from any RPCs that returned it.