rpc, wallet, test: fix invalid JSON in HelpExampleRpc curl examples

Several HelpExampleRpc call sites reused CLI-style argument strings
verbatim (missing commas, bare unquoted words, or single backslashes
that are not valid JSON escapes), producing curl examples that fail
JSON parsing as documented. Also fixes a stray trailing quote in the
restorewallet named-argument examples, a missing comma in the
listunspent example, and a wrong-schema string-instead-of-array
listunspent argument caught in review.

Lines touched are converted to raw string literals (or strprintf with a
raw string template) throughout, for consistency and to avoid manual
quote/backslash escaping.

Adds a regression check to rpc_help.py::dump_help() so this class of
bug can't silently reappear.

test/functional/rpc_help.py

@@ -8,6 +8,7 @@ from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error
 
 from collections import defaultdict
+import json
 import os
 import re
 
@@ -153,9 +154,17 @@ class HelpRpcTest(BitcoinTestFramework):
         os.mkdir(dump_dir)
         calls = [line.split(' ', 1)[0] for line in self.nodes[0].help().splitlines() if line and not line.startswith('==')]
         for call in calls:
+            help_text = self.nodes[0].help(call)
             with open(os.path.join(dump_dir, call), 'w') as f:
                 # Make sure the node can generate the help at runtime without crashing
-                f.write(self.nodes[0].help(call))
+                f.write(help_text)
+            # Make sure any curl examples have a JSON-RPC payload that is valid JSON
+            for match in re.finditer(r"--data-binary '(.*)' -H", help_text):
+                payload = match.group(1)
+                try:
+                    json.loads(payload)
+                except json.JSONDecodeError as e:
+                    raise AssertionError(f"HelpExampleRpc for '{call}' is not valid JSON: {payload!r}\n{e}")
 
     def wallet_help(self):
         assert 'getnewaddress ( "label" "address_type" )' in self.nodes[0].help('getnewaddress')