As per #162 and #695, we've decided that Winit should support clipboard handling. This issue is intended to house discussion on the API.

Discussion points:

• In most cases, data that can be copied can also be dragged and dropped. To what extent should this be unified with the drag/drop API?
• Clipboards can contain quite a few types of content (e.g. text, images, sounds, files). How do we want to handle these clipboard data formats? When do we want to distinguish between formats, and when do we want to map multiple OS formats onto one exposed format?
  • Additionally, some OSes support data sub-types. How do we want to expose those?
    • Windows lets you copy HTML snippets for rich text, and Wayland supports full MIME specification.
• Oftentimes, clipboard data can include the same data in multiple formats (e.g. words in a plain-text vs a rich-text format). How do we handle this?
  • Similarly, how do we allow people to upload the same data in different formats to the clipboard?