Added API method in window - captureWindow

[WannaCry016]

Description

This pull request introduces functionality for the neutralino.window.captureScreen(filepath) method, which captures the current application window and saves it as a screenshot to the specified file path. This functionality is fully implemented for Windows and Linux, with error handling and fallback mechanisms.

Changes proposed

• Implemented screen capture functionality for Windows using GDI+ with fallback to BitBlt.
• Enhanced Linux support with GTK for screen capturing.
• Added error handling and informative log messages for troubleshooting.
• Added test suite for captureScreen method.

How to test it

• Run the application and call the neutralino.window.captureScreen("screenshot.png") function.
• Verify the output:
  • Ensure a screenshot.png file is saved in the specified directory.
  • Check the content of the screenshot to ensure it reflects the application window.
• Test on both Windows and Linux platforms:
  • Windows: Ensure that PrintWindow or BitBlt is used for capturing the screen.
  • Linux: Verify the GTK functionality for capturing the screen.

Next steps

Extend the captureScreen functionality to support macOS.

Deploy notes

The changes are backward-compatible and do not impact other features.