Merge branch 'gl-dropdown-enter-key-fix' into 'master'

Fixed dropdown enter key when searching

## What does this MR do?

When searching in a dropdown you can now just press the enter key to trigger a click on the first row rather than having to press the down key & then enter.

## What are the relevant issue numbers?

Closes #19741 

See merge request !5231

CHANGELOG

@@ -47,6 +47,7 @@ v 8.10.0 (unreleased)
   - Make images fit to the size of the viewport !4810
   - Fix check for New Branch button on Issue page !4630 (winniehell)
   - Fix GFM autocomplete not working on wiki pages
+  - Fixed enter key not triggering click on first row when searching in a dropdown
   - Fix MR-auto-close text added to description. !4836
   - Support U2F devices in Firefox. !5177
   - Fix issue, preventing users w/o push access to sort tags !5105 (redetection)

app/assets/javascripts/gl_dropdown.js.coffee

@@ -210,9 +210,22 @@ class GitLabDropdown
         data: =>
           return @fullData
         callback: (data) =>
-          currentIndex = -1
           @parseData data
 
+          unless @filterInput.val() is ''
+            selector = '.dropdown-content li:not(.divider):visible'
+
+            if @dropdown.find('.dropdown-toggle-page').length
+              selector = ".dropdown-page-one #{selector}"
+
+            $(selector, @dropdown)
+              .first()
+              .find('a')
+              .addClass('is-focused')
+
+            currentIndex = 0
+
+
     # Event listeners
 
     @dropdown.on "shown.bs.dropdown", @opened