narrow: Support string and integer encoding of "id" operator.

Expands support for the message ID operand for id" operator to be either
a string or an integer. Previously, this operand was always validated as
a string.

api_docs/changelog.md

@@ -20,6 +20,16 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 8.0
 
+**Feature level 194**
+
+* [`GET /messages`](/api/get-messages),
+  [`GET /messages/matches_narrow`](/api/check-messages-match-narrow),
+  [`POST /message/flags/narrow`](/api/update-message-flags-for-narrow),
+  [`POST /register`](/api/register-queue):
+  For [search/narrow filters](/api/construct-narrow) with the `id`
+  operator, added support for encoding the message ID operand as either
+  a string or an integer. Previously, only string encoding was supported.
+
 **Feature level 193**
 
 * [`POST /messages/{message_id}/reactions`](/api/add-reaction),

api_docs/construct-narrow.md

@@ -65,12 +65,33 @@ filters did.
 
 ## Narrows that use IDs
 
+### Message IDs
+
 The `near` and `id` operators, documented in the help center, use message
 IDs for their operands.
 
 * `near:12345`: Search messages around the message with ID `12345`.
 * `id:12345`: Search for only message with ID `12345`.
 
+The message ID operand for the `id` operator may be encoded as either a
+number or a string. The message ID operand for the `near` operator must
+be encoded as a string.
+
+**Changes**: Prior to Zulip 8.0 (feature level 194), the message ID
+operand for the `id` operator needed to be encoded as a string.
+
+
+```json
+[
+    {
+        "operator": "id",
+        "operand": 12345
+    }
+]
+```
+
+### Stream and user IDs
+
 There are a few additional narrow/search options (new in Zulip 2.1)
 that use either stream IDs or user IDs that are not documented in the
 help center because they are primarily useful to API clients: