Enabled remote filter in compare dropdowns

Previously if the project had more than 100 branches or tags it wouldnt display them even after searching.
This now correctly sends an AJAx request to the backend to search for the branches/tags

Closes #29545

app/assets/javascripts/compare_autocomplete.js

@@ -18,7 +18,8 @@ window.CompareAutocomplete = (function() {
           return $.ajax({
             url: $dropdown.data('refs-url'),
             data: {
-              ref: $dropdown.data('ref')
+              ref: $dropdown.data('ref'),
+              search: term,
             }
           }).done(function(refs) {
             return callback(refs);
@@ -26,7 +27,7 @@ window.CompareAutocomplete = (function() {
         },
         selectable: true,
         filterable: true,
-        filterByText: true,
+        filterRemote: true,
         fieldName: $dropdown.data('field-name'),
         filterInput: 'input[type="search"]',
         renderRow: function(ref) {

spec/features/projects/compare_spec.rb

@@ -26,6 +26,14 @@ describe "Compare", js: true do
       click_button "Compare"
       expect(page).to have_content "Commits"
     end
+
+    it "filters branches" do
+      select_using_dropdown("from", "wip")
+
+      find(".js-compare-from-dropdown .compare-dropdown-toggle").click
+
+      expect(find(".js-compare-from-dropdown .dropdown-content")).to have_selector("li", count: 3)
+    end
   end
 
   describe "tags" do