Custom editors handled storing data to the clipboard on their own,
so the datainclipboard trigger was missing for some functionality.
H5P.clipboardify() however doesn't cope with additional information
that the custom editors can deal with.
Custom editors that prepare their own clipboard data can now use
H5P.setClipboard() directly and set their data while other elements
will be informed about the clipboard change.
Also relevant for HFP-2111 and HFP-2112.
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