Merge bitcoin/bitcoin#30238: json-rpc 2.0 followups: docs, tests, cli

1f6ab1215b minor: remove unnecessary semicolons from RPC content type examples (Matthew Zipkin)
b225295298 test: use json-rpc 2.0 in all functional tests by default (Matthew Zipkin)
391843b029 bitcoin-cli: use json-rpc 2.0 (Matthew Zipkin)
d39bdf3397 test: remove unused variable in interface_rpc.py (Matthew Zipkin)
0ead71df8c doc: update and link for JSON-RPC 2.0 (Matthew Zipkin)

Pull request description:

  This is a follow-up to #27101.

  - Addresses [post-merge comments ](https://github.com/bitcoin/bitcoin/pull/27101#discussion_r1606723428)
  - bitcoin-cli uses JSON-RPC 2.0
  - functional tests use JSON-RPC 2.0 by default (exceptions are in the regression tests added by #27101)

ACKs for top commit:
  tdb3:
    ACK 1f6ab1215b
  cbergqvist:
    ACK 1f6ab1215b

Tree-SHA512: 49bf14c70464081280216ece538a2f5ec810bac80a86a83ad3284f0f1b017edf755a1a74a45be279effe00218170cafde7c2de58aed07097a95c2c6b837a6b6c

doc/JSON-RPC-interface.md

@@ -33,10 +33,10 @@ requests when multiple wallets are in use.
 
 ```sh
 # Get block count from the / endpoint when rpcuser=alice and rpcport=38332
-$ curl --user alice --data-binary '{"jsonrpc": "1.0", "id": "0", "method": "getblockcount", "params": []}' -H 'content-type: application/json;' localhost:38332/
+$ curl --user alice --data-binary '{"jsonrpc": "2.0", "id": "0", "method": "getblockcount", "params": []}' -H 'content-type: application/json' localhost:38332/
 
 # Get balance from the /wallet/walletname endpoint when rpcuser=alice, rpcport=38332 and rpcwallet=desc-wallet
-$ curl --user alice --data-binary '{"jsonrpc": "1.0", "id": "0", "method": "getbalance", "params": []}' -H 'content-type: application/json;' localhost:38332/wallet/desc-wallet
+$ curl --user alice --data-binary '{"jsonrpc": "2.0", "id": "0", "method": "getbalance", "params": []}' -H 'content-type: application/json' localhost:38332/wallet/desc-wallet
 
 ```
 
@@ -80,7 +80,7 @@ The server recognizes [JSON-RPC v2.0](https://www.jsonrpc.org/specification) req
 and responds accordingly. A 2.0 request is identified by the presence of
 `"jsonrpc": "2.0"` in the request body. If that key + value is not present in a request,
 the legacy JSON-RPC v1.1 protocol is followed instead, which was the only available
-protocol in previous releases.
+protocol in v27.0 and prior releases.
 
 || 1.1 | 2.0 |
 |-|-|-|
@@ -88,7 +88,7 @@ protocol in previous releases.
 | Response marker | (none) | `"jsonrpc": "2.0"` |
 | `"error"` and `"result"` fields in response | both present | only one is present |
 | HTTP codes in response | `200` unless there is any kind of RPC error (invalid parameters, method not found, etc) | Always `200` unless there is an actual HTTP server error (request parsing error, endpoint not found, etc) |
-| Notifications: requests that get no reply | (not supported) | Supported for requests that exclude the "id" field |
+| Notifications: requests that get no reply | (not supported) | Supported for requests that exclude the "id" field. Returns HTTP status `204` "No Content" |
 
 ## Security
 

doc/release-notes-27101.md

@@ -2,8 +2,5 @@ JSON-RPC
 --------
 
 The JSON-RPC server now recognizes JSON-RPC 2.0 requests and responds with
-strict adherence to the specification (https://www.jsonrpc.org/specification):
-
-- Returning HTTP "204 No Content" responses to JSON-RPC 2.0 notifications instead of full responses.
-- Returning HTTP "200 OK" responses in all other cases, rather than 404 responses for unknown methods, 500 responses for invalid parameters, etc.
-- Returning either "result" fields or "error" fields in JSON-RPC responses, rather than returning both fields with one field set to null.
+strict adherence to the [specification](https://www.jsonrpc.org/specification).
+See [JSON-RPC-interface.md](/doc/JSON-RPC-interface.md#json-rpc-11-vs-20) for details.