desktop: simplify interface for view raise/focus

desktop: simplify interface for view raise/focus

Split desktop_focus_view() into the following two functions:
  - desktop_focus_and_activate_view()
  - desktop_raise_view()

Always call view_set_activated() rather than using the private
set_activated(). This keeps the code cleaner and ensures
wlr_foreign_toplevel_handle_v1_set_activated() is called.