ts: Migrate narrow_error to TypeScript.

This commit migrates narrow_error.js to TypeScript by inferring the
required types in the file and defining types in types.ts.

web/src/narrow_error.js

@@ -1,10 +0,0 @@
-import render_empty_feed_notice from "../templates/empty_feed_notice.hbs";
-
-export function narrow_error(narrow_banner_data) {
-    const title = narrow_banner_data.title;
-    const html = narrow_banner_data.html;
-    const search_data = narrow_banner_data.search_data;
-
-    const empty_feed_notice = render_empty_feed_notice({title, html, search_data});
-    return empty_feed_notice;
-}

web/src/narrow_error.ts

@@ -0,0 +1,28 @@
+import render_empty_feed_notice from "../templates/empty_feed_notice.hbs";
+
+type QueryWord = {
+    query_word: string;
+    is_stop_word: boolean;
+};
+
+type SearchData = {
+    query_word: QueryWord[];
+    has_stop_word: boolean;
+    stream_query?: string;
+    topic_query?: string;
+};
+
+type NarrowBannerData = {
+    title: string;
+    html?: string;
+    search_data?: SearchData;
+};
+
+export function narrow_error(narrow_banner_data: NarrowBannerData): string {
+    const title = narrow_banner_data.title;
+    const html = narrow_banner_data.html;
+    const search_data = narrow_banner_data.search_data;
+
+    const empty_feed_notice = render_empty_feed_notice({title, html, search_data});
+    return empty_feed_notice;
+}