Fix dropdowns showing keyboard on mobile even harder

osu.Framework/Graphics/UserInterface/DropdownSearchBar.cs

@@ -73,9 +73,17 @@ protected override void LoadComplete()
         public void ObtainFocus()
         {
             // On mobile platforms, let's not make the keyboard popup unless the dropdown is intentionally searchable.
+            // Unfortunately it is not enough to just early-return here,
+            // as even despite that the text box will receive focus via the text box input manager;
+            // it is necessary to cut off the text box input manager from parent input entirely.
+            // TODO: preferably figure out a better way to do this.
             bool willShowOverlappingKeyboard = host?.OnScreenKeyboardOverlapsGameWindow == true;
+
             if (willShowOverlappingKeyboard && !AlwaysDisplayOnFocus)
+            {
+                textBoxInputManager.UseParentInput = false;
                 return;
+            }
 
             textBoxInputManager.ChangeFocus(textBox);
             obtainedFocus = true;