msglist: Handle topic permalinks (/with/<id>) just as we do /near/ links

Explanation in a comment, which quotes Greg in zulip#5866.

Fixes: zulip#5866

src/message/messagesActions.js

@@ -257,7 +257,9 @@ export const messageLinkPress =
         return;
       }
 
-      const nearOperand = getNearOperandFromLink(parsedUrl, auth.realm);
+      const nearOperand =
+        getNearOperandFromLink(parsedUrl, auth.realm)
+        ?? getNearOperandFromLink(parsedUrl, auth.realm, { actuallyWith: true });
 
       if (!isNarrowValid(state, narrow)) {
         // E.g., a stream that's hidden from our user (perhaps doesn't exist).

src/utils/internalLinks.js

@@ -203,8 +203,22 @@ export const getNarrowFromNarrowLink = (
 /**
  * From a URL and realm with `isNarrowLink(url, realm) === true`, give
  *   message_id if the URL has /near/{message_id}, otherwise give null.
+ *
+ * HACK: to check for the new 'with' operator instead of 'near' (#5866),
+ *   pass `actuallyWith: true`. Quoting Greg from #5866:
+ *   > Currently the app doesn't interpret the "anchor" meaning of `/near/`
+ *   > links at all (that's #3604) — we already effectively give `/near/`
+ *   > links exactly the meaning that the upcoming `/with/` links will have.
+ *   > So to handle the new links, we just need to parse them and then
+ *   > handle them the way we already handle `/near/` links.
  */
-export const getNearOperandFromLink = (url: URL, realm: URL): number | null => {
+export const getNearOperandFromLink = (
+  url: URL,
+  realm: URL,
+  options: {| actuallyWith?: boolean |} = Object.freeze({}),
+): number | null => {
+  const { actuallyWith = false } = options;
+
   // isNarrowLink(…) is true, by jsdoc, so this call is OK.
   const hashSegments = getHashSegmentsFromNarrowLink(url, realm);
 
@@ -217,7 +231,7 @@ export const getNearOperandFromLink = (url: URL, realm: URL): number | null => {
       i % 2 === 0
       // The operator is 'near' and its meaning is not negated (`str` does
       // not start with "-").
-      && str === 'near',
+      && str === (actuallyWith ? 'with' : 'near'),
   );
   if (nearOperatorIndex < 0) {
     return null;