Don't move the cursor to the top of the page after closing a dialog

And other focus behavior fixes.

ve.ce.Surface.prototype.focus:
* Restore focus to the pasteTarget if a focusedNode was selected.
  This function is invoked when a dialog is closed, and we were
  always focusing the documentNode, which means the selection was
  restored incorrectly when the selection was really in the pasteTarget.

ve.ce.Surface.prototype.documentOnFocus:
* Don't rerender the model selection if the documentNode was focused but
  a focusedNode is selected. Otherwise the user can never deselect a
  focusedNode.

ve.ce.Surface.prototype.onModelSelect:
* Rerender the selection even if prev === next. This function was
  already called as a means to rerender a lost selection, and it didn't
  work if it so happened that the selection was still the same and was
  on a focusedNode.
* Clear the surfaceObserver state when moving focus from the
  documentNode to the pasteTarget. If we don't do this, then placing
  the selection back in the documentNode at the exact same place where
  it was before will not be noticed by the observer.

ve.ui.Context.prototype.onSurfaceFocus:
* Hide the context only when an inspector is open, not just when the
  context popup is visible. This ensures that the context is still
  hidden when the user clicks out of an inspector, but fixes a bug
  where the context was hidden when the selection was restored on
  an inspectable focusedNode.

Bug: 58090
Change-Id: I0658f025a9c6005d769fd0291380fcb9c1ba4f32
(cherry picked from commit 29532f15dba543f4c8013dce725b990ea924d193)