Add a windows specific method for setting the window icons based on the embedded exe icon.

Description

Using the following code you can get the icon for the running process, then call WM_SETICON to apply it to any window.
This prevents storing duplicate copies of the icon just to also reuse it for the window icon.

        let Ok(path) = std::env::current_exe() else {
            return 0;
        };

        let Ok(path) = U16CString::from_os_str(path.as_os_str()) else {
            return 0;
        };

        // SAFETY:
        // Path is checked to be a valid u16cstring above. The result is checked for errors where
        // 1 = not an icon or exe.
        // 0 = any other error.
        // While this obviously leaks the icon, the icon won't change for the lifetime of the program and can be used in more
        // than one window during the lifetime of the program.
        let icon = unsafe { ExtractIconW(GetModuleHandleW(std::ptr::null()), path.as_ptr(), 0) };

        if icon as usize <= 1 {
            return 0;
        }

Relevant platforms

Windows

Start from the issue's Windows example using current_exe, GetModuleHandleW, ExtractIconW, and WM_SETICON. Trace the existing window-icon APIs and add a Windows-specific method that reuses the embedded executable icon for a window, with behavior matching the requested icon application.