settings: Fix code for updating realm default language.

This commit fixes the bug when updating realm default
language setting by adding data-setting-widget-type
attribute to the relevant element with "prop-element"
class as get_input_element_value now expects every
element passed to it to have that attr after 64c8262eaf.

As a result we can now remove the code from
get_complete_data_for_subsection to handle realm
default language and just let get_input_element_value
handle it and it also helps in passing the parameter
unnecessary to request when the setting is not changed.

web/src/settings_components.ts

@@ -726,6 +726,8 @@ export function get_input_element_value(
             return get_dropdown_list_widget_setting_value($input_elem);
         case "field-data-setting":
             return get_field_data_input_value($input_elem);
+        case "language-setting":
+            return $input_elem.find(".language_selection_button span").attr("data-language-code");
         default:
             return undefined;
     }

web/src/settings_org.js

@@ -880,11 +880,6 @@ export function register_save_discard_widget_handlers(
         let data = {};
 
         switch (subsection) {
-            case "notifications":
-                data.default_language = $(
-                    "#org-notifications .language_selection_widget .language_selection_button span",
-                ).attr("data-language-code");
-                break;
             case "join_settings": {
                 const org_join_restrictions = $("#id_realm_org_join_restrictions").val();
                 switch (org_join_restrictions) {

web/templates/settings/language_selection_widget.hbs

@@ -1,4 +1,4 @@
-<div class="language_selection_widget input-group prop-element" id="id_{{section_name}}">
+<div class="language_selection_widget input-group prop-element" id="id_{{section_name}}" data-setting-widget-type="language-setting">
     <label class="settings-field-label">
         {{section_title}}
         {{#if help_link_widget_link}}