Merge #19396: refactor: Remove confusing OutputType::CHANGE_AUTO

fa927ff884 Enable Wswitch for OutputType (MarcoFalke)
faddad71f6 Remove confusing OutputType::CHANGE_AUTO (MarcoFalke)
fa2eb38352 interfaces: Remove unused getDefaultChangeType (MarcoFalke)

Pull request description:

  `OutputType::CHANGE_AUTO` is problematic for several reasons:

  * An output that is not change must never be described by `CHANGE_AUTO`. Simply allowing that option makes the code confusing and review harder than it needs to be.
  * To make review even harder, `CHANGE_AUTO` requires `-Wswitch` to be disabled for `OutputType`

  Fix both issues by removing `CHANGE_AUTO` and then enabling `-Wswitch` for `OutputType`

ACKs for top commit:
  promag:
    Code review ACK fa927ff884.
  laanwj:
    Code review ACK fa927ff884

Tree-SHA512: 24fd809757aa343866c94dafe9a7130b50cda4f77c97666d407f99b813f75b115a7d8e688a6bc2a737e87cba64ddd4e43f2b3c5538fd35fabb5845807bb39134

src/wallet/scriptpubkeyman.cpp

@@ -1900,8 +1900,8 @@ bool DescriptorScriptPubKeyMan::SetupDescriptorGeneration(const CExtKey& master_
         desc_prefix = "wpkh(" + xpub + "/84'";
         break;
     }
-    default: assert(false);
-    }
+    } // no default case, so the compiler can warn about missing cases
+    assert(!desc_prefix.empty());
 
     // Mainnet derives at 0', testnet and regtest derive at 1'
     if (Params().IsTestChain()) {