json_patch: fix move/copy false rejection between sibling keys sharing a prefix

json_patch_apply_move_copy() checks that "from" is not a proper prefix
of "path" per RFC 6902 section 4.4 (a location cannot be moved into one
of its own children), but it did so with a plain strncmp() over the raw
pointer strings, without checking that the shared run of characters
actually ends on a JSON Pointer reference-token boundary in "path".

As a result, moving or copying between two sibling object keys where
one name is a textual prefix of the other, e.g. "/aa" to "/aab", was
rejected with "Invalid attempt to move parent under a child" even
though "/aa" is not an ancestor pointer of "/aab" at all, just an
unrelated key that happens to share a few leading characters.

The fix requires that the character in "path" right after the shared
"from" prefix be either the end of the string (equal paths, a no-op)
or a '/' (a genuine nested reference token), before treating it as an
attempt to move a location under its own descendant.

Added two cases to json_patch_tests.json covering the move and copy
operations between such sibling keys, and refreshed the corresponding
golden test_json_patch.expected output.

tests/test_json_patch.expected

@@ -100,6 +100,8 @@ Testing 'Test the whole document, no match', doc '{ "foo": 1 }' patch '[ { "op":
 Testing 'Empty-string element', doc '{ "": 1 }' patch '[ { "op": "test", "path": "\/", "value": 1 } ]' : OK
 Testing '(null)', doc '{ "foo": [ "bar", "baz" ], "": 0, "a\/b": 1, "c%d": 2, "e^f": 3, "g|h": 4, "i\\j": 5, "k\"l": 6, " ": 7, "m~n": 8 }' patch '[ { "op": "test", "path": "\/foo", "value": [ "bar", "baz" ] }, { "op": "test", "path": "\/foo\/0", "value": "bar" }, { "op": "test", "path": "\/", "value": 0 }, { "op": "test", "path": "\/a~1b", "value": 1 }, { "op": "test", "path": "\/c%d", "value": 2 }, { "op": "test", "path": "\/e^f", "value": 3 }, { "op": "test", "path": "\/g|h", "value": 4 }, { "op": "test", "path": "\/i\\j", "value": 5 }, { "op": "test", "path": "\/k\"l", "value": 6 }, { "op": "test", "path": "\/ ", "value": 7 }, { "op": "test", "path": "\/m~0n", "value": 8 } ]' : OK
 Testing 'Move to same location has no effect', doc '{ "foo": 1 }' patch '[ { "op": "move", "from": "\/foo", "path": "\/foo" } ]' : OK
+Testing 'Move between sibling keys sharing a name prefix is not a parent/child move', doc '{ "aa": 1, "aab": 2 }' patch '[ { "op": "move", "from": "\/aa", "path": "\/aab" } ]' : OK
+Testing 'Copy between sibling keys sharing a name prefix is not a parent/child move', doc '{ "aa": 1, "aab": 2 }' patch '[ { "op": "copy", "from": "\/aa", "path": "\/aab" } ]' : OK
 Testing '(null)', doc '{ "foo": 1, "baz": [ { "qux": "hello" } ] }' patch '[ { "op": "move", "from": "\/foo", "path": "\/bar" } ]' : OK
 Testing '(null)', doc '{ "baz": [ { "qux": "hello" } ], "bar": 1 }' patch '[ { "op": "move", "from": "\/baz\/0\/qux", "path": "\/baz\/1" } ]' : OK
 Testing '(null)', doc '{ "baz": [ { "qux": "hello" } ], "bar": 1 }' patch '[ { "op": "copy", "from": "\/baz\/0", "path": "\/boo" } ]' : OK