Export DND related definitions

[johanneswilm]

Hey,
in Input Events [1] we refer to multiple drag and drop related definitions. As we try to move to the [=xref=] syntax, we notice that several of these are not being exported [2]. So currently we are linking to the following using the data-cite-attribute:

html/dnd.html#drag-data-store
html/dnd.html#the-drag-data-item-kind
html/dnd.html#concept-dnd-ro
html/dnd.html#the-drag-data-item-type-string
html/dnd.html#drag-data-store-item-list

[1] https://github.com/w3c/input-events

[2] w3c/input-events#129

[annevk]

Could you create a PR? For most of these adding the relevant export and for attributes should be sufficient I think. Seems like this would be relevant for the Clipboard API specification as well.