feat: Add support for disabling specific virtual keyboard keys with customizable appearance.

[bariskodas]

feat: Key Interaction Control (Enabled Keys Whitelist)

Summary

This PR implements a robust key interaction control system based on a whitelist approach. It introduces enabledKeys to VirtualKeyboardController, allowing developers to restrict keyboard input to a specific set of keys.

🚀 Features & Changes

API Refactor (Based on Feedback)

• Moved Logic to Controller: The disabledKeys parameter was removed from the widget. Instead, enabledKeys (Set<VirtualKeyboardKey>?) is now a property of VirtualKeyboardController.
• Whitelist Logic:
  • null: All keys are enabled (default).
  • Set<...>: Only keys in the set are interactive. Use this to restrict input (e.g. for a game or validation).
• Special Key Support: Special keys (Enter, Backspace) can now be controlled via this API, offering full flexibility.

🛠 Implementation Details

• Overlay Protection: Added logic to ensuring the key overlay (popup) is hidden immediately if a key becomes disabled while being pressed, preventing "stuck" UI states.
• Type Safety: Used Set<VirtualKeyboardKey> to ensure type safety and eliminate string parsing overhead during render.
• Theming: Retained the previous theming support (disabledBackgroundColor, disabledForegroundColor) to visually distinguish disabled keys.

Verification

• Static Analysis: Passed dart analyze.
• Manual Testing: Verified "Restrict Keys" demo in the example app.
• Edge Case: Verified overlay hides when key is disabled during press.

Usage Example

final controller = VirtualKeyboardController(
  layout: EnglishQwertyKeyboardLayout(),
  onKeyPress: (key) => ...,
  // Only enable specific keys. All others will be disabled.
  enabledKeys: {
    VirtualKeyboardKey.a,
    VirtualKeyboardKey.b,
    VirtualKeyboardKey.backspace,
  },
);

[bariskodas]

@orkun1675 could you review? ⚡️