Use language primitive types.

.editorconfig

···
 #Roslyn language styles
 
 #Style - type names
-dotnet_style_predefined_type_for_locals_parameters_members = true:silent
-dotnet_style_predefined_type_for_member_access = true:silent
+dotnet_style_predefined_type_for_locals_parameters_members = true:warning
+dotnet_style_predefined_type_for_member_access = true:warning
 csharp_style_var_when_type_is_apparent = true:none
 csharp_style_var_for_built_in_types = true:none
 csharp_style_var_elsewhere = true:silent

osu.Framework.Tests/Visual/Input/TestSceneInputManager.cs

···
 // Copyright (c) ppy Pty Ltd <[e-mail]>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System;
 using osu.Framework.Allocation;
 using osu.Framework.Configuration;
 using osu.Framework.Graphics;
···
                 var currentState = inputManager.CurrentState;
                 var mouse = currentState.Mouse;
                 inputManagerStatus.Text = $"{inputManager}";
-                mouseStatus.Text = $"Mouse: {mouse.Position} {mouse.Scroll} " + String.Join(" ", mouse.Buttons);
-                keyboardStatus.Text = "Keyboard: " + String.Join(" ", currentState.Keyboard.Keys);
-                joystickStatus.Text = "Joystick: " + String.Join(" ", currentState.Joystick.Buttons);
+                mouseStatus.Text = $"Mouse: {mouse.Position} {mouse.Scroll} " + string.Join(" ", mouse.Buttons);
+                keyboardStatus.Text = "Keyboard: " + string.Join(" ", currentState.Keyboard.Keys);
+                joystickStatus.Text = "Joystick: " + string.Join(" ", currentState.Joystick.Buttons);
                 base.Update();
             }
 

osu.Framework/Audio/Track/ITrackStore.cs

···
 // Copyright (c) ppy Pty Ltd <[e-mail]>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System;
-
 namespace osu.Framework.Audio.Track
 {
     public interface ITrackStore : IAdjustableResourceStore<Track>
···
         /// </summary>
         /// <param name="length">The length of the virtual track.</param>
         /// <returns>A new virtual track.</returns>
-        Track GetVirtual(double length = Double.PositiveInfinity);
+        Track GetVirtual(double length = double.PositiveInfinity);
     }
 }

osu.Framework/Input/States/ButtonStates.cs

···
 // Copyright (c) ppy Pty Ltd <[e-mail]>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
···
             pressedButtons.AddRange(other.pressedButtons);
         }
 
-        public override string ToString() => $@"{GetType().ReadableName()}({String.Join(" ", pressedButtons)})";
+        public override string ToString() => $@"{GetType().ReadableName()}({string.Join(" ", pressedButtons)})";
 
         public IEnumerator<TButton> GetEnumerator() => ((IEnumerable<TButton>)pressedButtons).GetEnumerator();
         IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();