Merge bitcoin/bitcoin#32845: rpc, test: Fix JSON parsing errors in unloadwallet and getdescriptoractivity RPCs

c5c1960f93 doc: Add release notes for changes in RPCs (pablomartin4btc)
90fd5acbe5 rpc, test: Fix error message in getdescriptoractivity (pablomartin4btc)
39fef1d203 test: Add missing logging info for each test (pablomartin4btc)
53ac704efd rpc, test: Fix error message in unloadwallet (pablomartin4btc)
1fc3a8e8e7 rpc, test: Add EnsureUniqueWalletName tests (pablomartin4btc)
b635bc0896 rpc, util: Add EnsureUniqueWalletName (pablomartin4btc)

Pull request description:

  Currently, `unloadwallet` RPC call fails with a JSON parsing error when no `wallet_name` argument is provided. This behavior is misleading because the error originates from a low-level JSON type mismatch, rather than clearly indicating that the wallet name or RPC endpoint (`-rpcwallet=...`) is missing. Also, found out that the [issue](https://github.com/bitcoin/bitcoin/pull/13111#issuecomment-398831543) was noticed during its implementation but never addressed.

  In addition, I've verified all RPC commands calls finding that `getdescriptoractivity` had the same problem, but related to the array input types (blockhashes & descriptors), so I've corrected that RPC as well. For consistency I've added the missing logging info for each test case in `test/functional/rpc_getdescriptoractivity.py` in preparation for the new test.

  **_-Before_**
  ```
  ./build/bin/bitcoin-cli -regtest -datadir=/tmp/btc unloadwallet
  error code: -3
  error message:
  JSON value of type number is not of expected type string
  ```
  ```
  ./build/bin/bitcoin-cli -regtest -datadir=/tmp/btc getdescriptoractivity
  error code: -3
  error message:
  JSON value of type null is not of expected type array
  ```
  ```
  ./build/bin/bitcoin-cli -regtest -datadir=/tmp/btc getdescriptoractivity '[]'
  error code: -3
  error message:
  JSON value of type null is not of expected type array
  ```
  **_-After_**
  ```
  ./build/bin/bitcoin-cli -regtest -datadir=/tmp/btc unloadwallet
  error code: -8
  error message:
  Either the RPC endpoint wallet or the wallet name parameter must be provided
  ```
  ```
  ./build/bin/bitcoin-cli -regtest -datadir=/tmp/btc getdescriptoractivity
  error code: -1
  error message:
  getdescriptoractivity ["blockhash",...] [scanobjects,...] ( include_mempool )

  Get spend and receive activity associated with a set of descriptors for a set of blocks. This command pairs well with the `relevant_blocks` output of `scanblocks()`.
  This call may take several minutes. If you encounter timeouts, try specifying no RPC timeout (bitcoin-cli -rpcclienttimeout=0)

  Arguments:
  1. blockhashes                   (json array, required) The list of blockhashes to examine for activity. Order doesn't matter. Must be along main chain or an error is thrown.

       [
         "blockhash",              (string) A valid blockhash
         ...
       ]
  2. scanobjects                   (json array, required) Array of scan objects. Every scan object is either a string descriptor or an object:
       [
         "descriptor",             (string) An output descriptor
         {                         (json object) An object with output descriptor and metadata
           "desc": "str",          (string, required) An output descriptor
           "range": n or [n,n],    (numeric or array, optional, default=1000) The range of HD chain indexes to explore (either end or [begin,end])
         },
         ...
       ]
  3. include_mempool               (boolean, optional, default=true) Whether to include unconfirmed activity

  ...
  ```
  ```
  ./build/bin/bitcoin-cli -regtest -datadir=/tmp/btc getdescriptoractivity '[]'
  error code: -1
  error message:
  getdescriptoractivity ["blockhash",...] [scanobjects,...] ( include_mempool )

  ...
  ```

ACKs for top commit:
  achow101:
    ACK c5c1960f93
  stickies-v:
    re-ACK c5c1960f93
  furszy:
    ACK c5c1960f93

Tree-SHA512: e831ff1acbfd15d2ce3a69bb408cce94664c0b63b2aa2f4627a05c6c052241ae3b5cc238219ef1b30afb489a4a3f4c3030e2168b0c8f08b4d20805d050d810f5

doc/release-notes-32845.md

@@ -0,0 +1,9 @@
+Updated RPCs
+------------
+
+- `unloadwallet` - Return RPC_INVALID_PARAMETER when both the RPC wallet endpoint
+and wallet_name parameters are unspecified. Previously the RPC failed with a JSON
+parsing error.
+- `getdescriptoractivity` - Mark blockhashes and scanobjects arguments as required,
+so the user receives a clear help message when either is missing. As in `unloadwallet`,
+previously the RPC failed with a JSON parsing error.