Implement a V2 password textbox (#38028)

This PR adds a password input form control consistent with the V2 form
controls.

Default state:

<img width="601" height="90" alt="image"
src="https://github.com/user-attachments/assets/f7e49468-8e9f-4a94-9c12-ad445b7cac17"
/>

Caps Lock active:

<img width="598" height="90" alt="image"
src="https://github.com/user-attachments/assets/cda4fb67-4803-4e39-9cbd-73f34318ab6f"
/>

---------

Co-authored-by: Bartłomiej Dach <dach.bartlomiej@gmail.com>

osu.Game.Tests/Visual/UserInterface/TestSceneFormControls.cs

@@ -235,6 +235,11 @@ namespace osu.Game.Tests.Visual.UserInterface
                                     Padding = new MarginPadding(10),
                                     Children = new Drawable[]
                                     {
+                                        new FormPasswordTextBox
+                                        {
+                                            Caption = "Password",
+                                            TabbableContentContainer = this,
+                                        },
                                         new FormNumberBox(allowDecimals: true)
                                         {
                                             Caption = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua",

osu.Game/Graphics/UserInterfaceV2/FormPasswordTextBox.cs

@@ -0,0 +1,106 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. 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.Graphics;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Input;
+using osu.Framework.Input.Events;
+using osu.Framework.Platform;
+using osu.Game.Graphics.Containers;
+using osu.Game.Graphics.UserInterface;
+using osu.Game.Localisation;
+using osuTK;
+using osuTK.Input;
+
+namespace osu.Game.Graphics.UserInterfaceV2
+{
+    public partial class FormPasswordTextBox : FormTextBox
+    {
+        private CapsWarning capsWarning = null!;
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            CaptionContainer.Add(capsWarning = new CapsWarning
+            {
+                Anchor = Anchor.TopRight,
+                Origin = Anchor.TopRight,
+                Alpha = 0,
+            });
+        }
+
+        internal override InnerTextBox CreateTextBox() => new InnerPasswordBox
+        {
+            UpdateCapsWarning = visible => capsWarning.FadeTo(visible ? 1 : 0, 250, Easing.OutQuint),
+        };
+
+        internal partial class InnerPasswordBox : InnerTextBox
+        {
+            public Action<bool>? UpdateCapsWarning { get; init; }
+
+            [Resolved]
+            private GameHost host { get; set; } = null!;
+
+            protected override Drawable GetDrawableCharacter(char c) => new FallingDownContainer
+            {
+                AutoSizeAxes = Axes.Both,
+                Child = new OsuPasswordTextBox.PasswordMaskChar(FontSize),
+            };
+
+            protected override bool AllowUniqueCharacterSamples => false;
+
+            public InnerPasswordBox()
+            {
+                InputProperties = new TextInputProperties(TextInputType.Password, false);
+            }
+
+            protected override bool OnKeyDown(KeyDownEvent e)
+            {
+                if (e.Key == Key.CapsLock)
+                    UpdateCapsWarning?.Invoke(host.CapsLockEnabled);
+
+                return base.OnKeyDown(e);
+            }
+
+            protected override void OnFocus(FocusEvent e)
+            {
+                UpdateCapsWarning?.Invoke(host.CapsLockEnabled);
+                base.OnFocus(e);
+            }
+
+            protected override void OnFocusLost(FocusLostEvent e)
+            {
+                UpdateCapsWarning?.Invoke(false);
+                base.OnFocusLost(e);
+            }
+        }
+
+        private partial class CapsWarning : OsuTextFlowContainer
+        {
+            public CapsWarning()
+                : base(t => t.Font = OsuFont.Style.Caption1)
+            {
+            }
+
+            [BackgroundDependencyLoader]
+            private void load(OsuColour colours)
+            {
+                AutoSizeAxes = Axes.Both;
+                Colour = colours.YellowLight;
+
+                AddArbitraryDrawable(new SpriteIcon
+                {
+                    Anchor = Anchor.BottomLeft,
+                    Origin = Anchor.BottomLeft,
+                    Size = new Vector2(10),
+                    Icon = FontAwesome.Solid.ExclamationTriangle,
+                    Margin = new MarginPadding { Right = 2 },
+                    Y = 1f,
+                });
+                AddText(CommonStrings.CapsLock);
+            }
+        }
+    }
+}

osu.Game/Graphics/UserInterfaceV2/FormTextBox.cs

@@ -84,6 +84,8 @@ namespace osu.Game.Graphics.UserInterfaceV2
         private FormFieldCaption caption = null!;
         private IFocusManager focusManager = null!;
 
+        protected Container CaptionContainer { get; private set; } = null!;
+
         [Resolved]
         private OverlayColourProvider colourProvider { get; set; } = null!;
 
@@ -104,12 +106,22 @@ namespace osu.Game.Graphics.UserInterfaceV2
                     Spacing = new Vector2(0, 4),
                     Children = new Drawable[]
                     {
-                        caption = new FormFieldCaption
+                        CaptionContainer = new Container
                         {
+                            RelativeSizeAxes = Axes.X,
+                            AutoSizeAxes = Axes.Y,
                             Anchor = Anchor.TopLeft,
                             Origin = Anchor.TopLeft,
-                            Caption = Caption,
-                            TooltipText = HintText,
+                            Children = new Drawable[]
+                            {
+                                caption = new FormFieldCaption
+                                {
+                                    Anchor = Anchor.TopLeft,
+                                    Origin = Anchor.TopLeft,
+                                    Caption = Caption,
+                                    TooltipText = HintText,
+                                },
+                            },
                         },
                         textBox = CreateTextBox().With(t =>
                         {

osu.Game/Localisation/CommonStrings.cs

@@ -170,9 +170,14 @@ namespace osu.Game.Localisation
         public static LocalisableString Exit => new TranslatableString(getKey(@"exit"), @"Exit");
 
         /// <summary>
-        /// "Caps lock is active"
+        /// "Caps Lock"
         /// </summary>
-        public static LocalisableString CapsLockIsActive => new TranslatableString(getKey(@"caps_lock_is_active"), @"Caps lock is active");
+        public static LocalisableString CapsLock => new TranslatableString(getKey(@"caps_lock"), @"Caps Lock");
+
+        /// <summary>
+        /// "Caps Lock is active"
+        /// </summary>
+        public static LocalisableString CapsLockIsActive => new TranslatableString(getKey(@"caps_lock_is_active"), @"Caps Lock is active");
 
         /// <summary>
         /// "Revert to default"