Fix issues with copy-pasting MWTransclusionNodes

ve.dm.MWTransclusionNode
* Implement getClonedElement to remove originalDomElements
  and originalMw. We don't want to put these in the clipboard
  as there is no guarantee they are the rendering of the current
  set of parameters (a refresh may be in progress) and they may
  confuse the converter on the way back in.
  Remove about attribute to prevent about grouping of duplicated
  nodes.
* Set an extra attribute to flag that the outputted DOM doesn't
  have any generated content attached to it that can be stored
  on load.
* Check for said attribute in toDataElement and skip the
  storeGeneratedContents step. This will trigger an async update
  of the generated contents on paste.

ve.ce.Surface
* Call cloneElements before writing to pasteTarget so data in external
  clipboard is stripped of generated contents.

ve.dm.Node
* Only strip data-parsoid as other attributes may be meaningful.

ve.dm.mwExample, ve.dm.Node.test
* Update tests

Bug: 58241
Change-Id: I3e15cc97e94747647078204a0b398e6ac3ec6382