invite: Display globe icon for web-public streams.

This requires both passing through the is_web_public parameter to the
template, and a bit of CSS to make the globe not huge.

static/js/stream_data.js

@@ -416,6 +416,7 @@ export function get_invite_stream_data() {
             name: sub.name,
             stream_id: sub.stream_id,
             invite_only: sub.invite_only,
+            is_web_public: sub.is_web_public,
             default_stream: default_stream_ids.has(sub.stream_id),
         };
     }

static/styles/zulip.css

@@ -2588,6 +2588,10 @@ textarea.invitee_emails {
 
 #invite-stream-checkboxes {
     padding-bottom: 26px;
+
+    i.zulip-icon-globe {
+        font-size: 80%;
+    }
 }
 
 #invite-method-choice {