tooltip: Add channel folder tooltip for truncated names in left sidebar.

There isn't a way to check the complete name for long truncated channel
folders name in the left sidebar.

This commit adds a tooltip for channel folder only when the folder names
are truncated in the left sidebar.

Fixes: zulip#35582.

web/src/left_sidebar_tooltips.ts

@@ -1,4 +1,5 @@
 import $ from "jquery";
+import assert from "minimalistic-assert";
 import * as tippy from "tippy.js";
 
 import * as drafts from "./drafts.ts";
@@ -223,4 +224,25 @@ export function initialize(): void {
         ].join(","),
         ...topic_visibility_policy_tooltip_props,
     });
+
+    tippy.delegate("body", {
+        target: ".stream-list-section-container .left-sidebar-title",
+        delay: LONG_HOVER_DELAY,
+        appendTo: () => document.body,
+        onShow(instance) {
+            const folder_name_element = instance.reference;
+            assert(folder_name_element instanceof HTMLElement);
+
+            if (folder_name_element.offsetWidth < folder_name_element.scrollWidth) {
+                const folder_name = folder_name_element.textContent ?? "";
+                instance.setContent(folder_name);
+                return undefined;
+            }
+
+            return false;
+        },
+        onHidden(instance) {
+            instance.destroy();
+        },
+    });
 }