DeskTop: Untangle menu state update for windows and shortcuts

* Update DeskTop's main loop to not check window validity and update
  menu item states on just a mouse move, since that can't change the
  application state. This allows the following changes without
  compromising performance.
* Back to the MouseDesk code, DeskTop had logic to conditionally
  refresh the "Selector" (now "Shortcut") menu item enable/disable
  states when the contents were modified, with a global flag. Since
  overall logic and performance has improved, just do this
  unconditionally.
* Update menu item states that require a window (e.g. "Close") and the
  View menu checkbox in the main loop, rather than requiring all
  places that might modify the state (e.g. window open, window close,
  view menu action) to make the right calls.

... and consolidate all of the updating logic into one proc, to ease
maintenance. The simplification saves ~100 bytes.

No functional changes - I hope!

desktop/desktop.s

@@ -31,7 +31,7 @@
         DEFSEG SegmentLoader,      $2000, $0200
         DEFSEG SegmentDeskTopAux,  $4000, $8000
         DEFSEG SegmentDeskTopLC,   $D000, $2100
-        DEFSEG SegmentDeskTopMain, $4000, $7900
+        DEFSEG SegmentDeskTopMain, $4000, $7800
         DEFSEG SegmentInitializer, $0800, $0900
         DEFSEG SegmentInvoker,     $0290, $0160
 

desktop/init.s

@@ -338,8 +338,6 @@ done:
         adc     selector_list_data_buf + kSelectorListNumSecondaryRunListOffset
         sta     num_selector_list_items
 
-        copy    #0, selector_menu_items_updated_flag
-
         lda     selector_list_data_buf
         sta     count
 L0A3B:  lda     index
@@ -997,12 +995,7 @@ unit_num:
         ;; Final MGTK configuration
         MGTK_CALL MGTK::CheckEvents
         MGTK_CALL MGTK::SetCursor, MGTK::SystemCursor::pointer
-        lda     #0
-        sta     active_window_id
-        jsr     main::UpdateWindowMenuItems
-        jsr     main::DisableMenuItemsRequiringVolumeSelection
-        jsr     main::DisableMenuItemsRequiringFileSelection
-        jsr     main::DisableMenuItemsRequiringSelection
+        copy    #0, active_window_id
 
         ;; Add desktop icons
         ldx     #0