* Fix#209158. Add Copy Output and Open Output in Text Editor to Scrollable text output context menu.
* Context menu should be triggered on container
* fix naming
* dataflow support for updated metadata
* update cellAttachmentRenderer.ts to reflect metadata being a getter() inside MarkupCell
* document paste additions
* update condition to re-render cells, now includes metadata changes
* paste API working, debugging command added
* paste working with metadata. needs numbering, and cleaning upon delete
* paste screenshot works fully
* remove debugging command. Cleaning.
* notebook cells now re-render upon metadata changes
* changed name validity checking, remove unneeded function
* use _document for cell data, use snippet choice, dto fix
* return subscription, for loop, uri fix, alter metadata in-place, better snippet
* metadata fix, object.equals, fix cellAttRenderer metadata call
* added comment with source of encodeBase64
* gate mkdn image paste behind experimental setting