This commit implements a new API for drag and drop, with a `DataTransfer` type which abstracts over the various clipboard/drag and drop APIs across different platforms. I built this on top of #2429 although admittedly I ended up removing pretty much all of their work while I was reworking the design.
This is being built in order to help support [drag-and-drop work](https://github.com/slint-ui/slint/issues/1967) in Slint's winit backend. As part of that work, I did extensive research on how drag-and-drop and clipboard APIs are implemented across different platforms, and wrote a (still WIP) research document that can be found [here](https://gist.github.com/eira-fransham/06750cf8d25ade08d362a0ca8dfafe06).
The new API is inspired by the browser's [`DataTransfer`](https://developer.mozilla.org/en-US/docs/Web/API/DataTransfer) API.
Added `Window::safe_area`, which describes the area of the surface that
is unobstructed by notches, bezels etc. The drawing code in the examples
have been updated to draw a star inside the safe area, and the plain
background outside of it.
Also renamed `Window::inner_position` to `Window::surface_position`, and
changed it to from screen coordinates to window coordinates, to better
align how these coordinate systems work together.
Finally, added some SVG images and documentation to describe how all of
this works.
This is fully implemented on macOS and iOS, and partially on the web.
Co-authored-by: daxpedda <daxpedda@gmail.com>
