refractor: Move get_visible_email from popovers.js to people.js.

This commit moves the get_visible_email function to people.js
as this function will be used in other places and people.js seems
relevant file for this.

Tests are added to get full coverage.

frontend_tests/node_tests/people.js

@@ -1056,3 +1056,27 @@ run_test('emails_strings_to_user_ids_array', function () {
     user_ids = people.emails_strings_to_user_ids_array('dummyuser@example.com');
     assert.equal(user_ids, undefined);
 });
+
+run_test('get_visible_email', function () {
+    const steven = {
+        email: 'steven@example.com',
+        delivery_email: 'steven-delivery@example.com',
+        user_id: 7,
+        full_name: 'Steven',
+    };
+
+    const maria = {
+        email: 'maria@example.com',
+        user_id: 728,
+        full_name: 'Maria',
+    };
+
+    people.add(steven);
+    people.add(maria);
+
+    let email = people.get_visible_email(steven);
+    assert.equal(email, steven.delivery_email);
+
+    email = people.get_visible_email(maria);
+    assert.equal(email, maria.email);
+});

static/js/people.js

@@ -102,6 +102,13 @@ exports.update_email = function (user_id, new_email) {
     // still work correctly.
 };
 
+exports.get_visible_email = function (user) {
+    if (user.delivery_email) {
+        return user.delivery_email;
+    }
+    return user.email;
+};
+
 exports.get_user_id = function (email) {
     const person = exports.get_by_email(email);
     if (person === undefined) {

static/js/popovers.js

@@ -149,13 +149,6 @@ function get_custom_profile_field_data(user, field, field_types, dateFormat) {
     return profile_field;
 }
 
-function get_visible_email(user) {
-    if (user.delivery_email) {
-        return user.delivery_email;
-    }
-    return user.email;
-}
-
 function render_user_info_popover(user, popover_element, is_sender_popover, private_msg_class,
                                   template_class, popover_placement) {
     const is_me = people.is_my_user_id(user.user_id);
@@ -184,7 +177,7 @@ function render_user_info_popover(user, popover_element, is_sender_popover, priv
         sent_by_uri: hash_util.by_sender_uri(user.email),
         show_email: settings_data.show_email(),
         show_user_profile: !(user.is_bot || page_params.custom_profile_fields.length === 0),
-        user_email: get_visible_email(user),
+        user_email: people.get_visible_email(user),
         user_full_name: user.full_name,
         user_id: user.user_id,
         user_last_seen_time_status: buddy_data.user_last_seen_time_status(user.user_id),
@@ -307,7 +300,7 @@ exports.show_user_profile = function (user) {
 
     const args = {
         full_name: user.full_name,
-        email: get_visible_email(user),
+        email: people.get_visible_email(user),
         profile_data: profile_data,
         user_avatar: "avatar/" + user.email + "/medium",
         is_me: people.is_current_user(user.email),