wasm: clipboard improvements

1. There is a trick to write multiple mime types to the clipboard. You only create one clipboard item with several entries. Don't try to create more than one clipboard item.

see here:

https://www.stefanjudis.com/notes/a-clipboard-magic-trick-how-to-use-different-mime-types-with-the-clipboard/

or my code fragment in attached file qwasmclipboard-writeToClipboardApi.cpp.

2. Actual it is not possible to write HTML and something else to the clipboard. If HTML is present, you discard everything else. It would by nice, to support all mime types.

3. Support for mime types with "application/..." is possible in some browsers as "web application/...".