In newer versions there is now a normal method for this which also supports
dynamically added components.

The static version is deprecated and removed in 2.0, so we need to port here.

This has proper support for rollup while providing the same API.

This is what open-wc recommends now and uses in their @open-wc/testing package

FileHandlingClipboard and FileSink depend on each other. Register
the later at runtime so we don't get a dependecy cycle for imports.

Remove duplicated clipboard warning, disable nextcloudfilepicker upload button if no files are selected

Otherwhise it will try to access it an error out when trying to open
the dialog.