windows: add builder method to make a tool window

[lunixbochs]

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

This adds the ability to make a window with the style WS_EX_TOOLWINDOW. This is the missing piece to be able to create borderless/transparent desktop overlay windows with winit that don't show up in the taskbar, don't animate on open/close, etc.

You can build a cross-platform window in this style like the following (I don't target Wayland so I don't have a Wayland example):

let builder = winit::window::WindowBuilder::new()
    .with_transparent(true)
    .with_decorations(false)
    .with_resizable(false)
    .with_title("Canvas");

#[cfg(target_os = "linux")]
let builder = builder
    .with_x11_window_type(vec![XWindowType::Utility])
    .with_override_redirect(true);
#[cfg(target_os = "windows")]
let builder = builder.with_tool_window(true);
#[cfg(target_os = "macos")]
let builder = builder.with_has_shadow(false);

(Anyone drawing a transparent window over the whole screen probably also cares about window.set_cursor_hittest(false) so they can click through it, which is why I just PR'd support for that on X11)