user_group_popover: Redesign popover using the new "popover-menu" theme.

As part of the popover menu redesign, this commit redesigns the user
group info popover using the new "popover-menu" tippy theme and improves
accessibility by using appropriate ARIA attributes.

Fixes part of #28699.

web/src/tippyjs.ts

@@ -300,6 +300,7 @@ export function initialize(): void {
             "#filter_streams_tooltip",
             ".error-icon-message-recipient .zulip-icon",
             "#personal-menu-dropdown .status-circle",
+            ".popover-group-menu-member-list .popover_user_presence",
             "#copy_generated_invite_link",
         ].join(","),
         appendTo: () => document.body,