tippy: Use namespace import for tippy.js.

Names like “delegate”, “Instance”, “Placement”, “Props”, and
“ReferenceElement” are much too generic to make sense as named
imports.

The downside is that we now need to write tippy.default(…) instead of
tippy(…) (because ES module namespace objects cannot be callable), but
that cost is worthwhile.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

web/src/compose_send_menu_popover.js

@@ -1,5 +1,5 @@
 import $ from "jquery";
-import {delegate} from "tippy.js";
+import * as tippy from "tippy.js";
 
 import render_send_later_popover from "../templates/popovers/send_later_popover.hbs";
 import render_send_later_modal from "../templates/send_later_modal.hbs";
@@ -142,7 +142,7 @@ export function toggle() {
 }
 
 export function initialize() {
-    delegate("body", {
+    tippy.delegate("body", {
         ...popover_menus.default_popover_props,
         target: "#send_later i",
         onUntrigger() {