Avalonia: remember size and position

[Gabriel Dufresne (GabrielDuf)]

This pull request introduces persistent window geometry management to the MainWindow in src/UniGetUI.Avalonia/Views/MainWindow.axaml.cs. The changes ensure that the window's size, position, and state are saved and restored across application restarts, and improve handling of DPI scaling and user interactions with the window. The most significant updates are grouped below:

Window Geometry Persistence:

• Added methods to save (SaveGeometryAsync, SaveGeometryNow) and restore (RestoreGeometry) the window's geometry (position, size, and maximized state) using the Settings system, including logic to verify restored bounds are visible on the current desktop configuration. These methods are called on window events such as resize, position change, and closing.

DPI and Window Minimum Size Handling (Windows-specific):

• Enhanced the Windows message handler to correctly calculate minimum window sizes by accounting for DPI scaling and window frame sizes, using new P/Invoke calls to GetDpiForWindow and AdjustWindowRectExForDpi.

User Interaction Improvements:

• Improved the title bar pointer handler to support double-clicking for maximize/restore and to avoid starting a drag unless the left mouse button is pressed.

fix issue #4799