Document copy-directory and related changes in manuals.

Document copy-directory and related changes in manuals.

* doc/emacs/buffers.texi (Misc Buffer): Move view-buffer to View Mode.

* doc/emacs/display.texi (View Mode): New node.  Move view-file here from
Misc File Ops.  Move view-buffer here from Misc Buffer.

* doc/emacs/files.texi (Misc File Ops): Document new
delete-by-moving-to-trash behavior.  Remove view-file.

* doc/lispref/files.texi (Changing Files, Create/Delete Dirs): Document new
arguments for delete-file, delete-directory, and copy-directory.