Create an OOUI editor widget


Create an OOUI editor widget

For now this exists in parallel to the old editor system,
and nothing uses it yet. We'll migrate things in follow-up
commits until the old system is unused and can be removed.

Notable changes:

  • Warning for anonymous editors is no longer a tooltip on the side, but now appears above the editor
  • Rename editor preference value 'none' to 'wikitext', and provide b/c logic in both directions
  • Add b/c logic in SwitchEditorAction
  • New VE integration uses one Target instance that is reused, rather than creating a new one every time
  • New system keeps focus when switching between editors

Bug: T103572
Bug: T97290
Bug: T101189
Change-Id: Ic2353ef6e9155bd921d224d129c7b70cb22ba8a7