Cleanup: remove unused window states, add doc-strings

Note that the GHOST_TWindowState is stored in DNA & that
values shouldn't be changed.

intern/ghost/GHOST_Types.h

@@ -170,14 +170,15 @@ typedef enum {
   GHOST_kModifierKeyNum
 } GHOST_TModifierKey;
 
+/**
+ * \note these values are stored in #wmWindow::windowstate,
+ * don't change, only add new values.
+ */
 typedef enum {
   GHOST_kWindowStateNormal = 0,
-  GHOST_kWindowStateMaximized,
-  GHOST_kWindowStateMinimized,
-  GHOST_kWindowStateFullScreen,
-  GHOST_kWindowStateEmbedded,
-  // GHOST_kWindowStateModified,
-  // GHOST_kWindowStateUnModified,
+  GHOST_kWindowStateMaximized = 1,
+  GHOST_kWindowStateMinimized = 2,
+  GHOST_kWindowStateFullScreen = 3,
 } GHOST_TWindowState;
 
 typedef enum {

intern/ghost/intern/GHOST_WindowWayland.cc

@@ -332,9 +332,6 @@ static bool gwl_window_state_set_for_libdecor(libdecor_frame *frame,
       libdecor_frame_set_fullscreen(frame, nullptr);
       break;
     }
-    case GHOST_kWindowStateEmbedded: {
-      return false;
-    }
   }
   return true;
 }
@@ -377,9 +374,6 @@ static bool gwl_window_state_set_for_xdg(xdg_toplevel *toplevel,
       xdg_toplevel_set_fullscreen(toplevel, nullptr);
       break;
     }
-    case GHOST_kWindowStateEmbedded: {
-      return false;
-    }
   }
   return true;
 }

source/blender/makesdna/DNA_windowmanager_types.h

@@ -269,7 +269,7 @@ typedef struct wmWindow {
   int winid;
   /** Window coords. */
   short posx, posy, sizex, sizey;
-  /** Borderless, full. */
+  /** Normal, maximized, full-screen, #GHOST_TWindowState. */
   char windowstate;
   /** Set to 1 if an active window, for quick rejects. */
   char active;

source/blender/windowmanager/intern/wm_window.c

@@ -109,7 +109,7 @@ static struct WMInitStruct {
   int size_x, size_y;
   int start_x, start_y;
 
-  int windowstate;
+  GHOST_TWindowState windowstate;
   eWinOverrideFlag override_flag;
 
   bool window_focus;
@@ -735,7 +735,6 @@ static void wm_window_ghostwindow_add(wmWindowManager *wm,
     /* Clear double buffer to avoids flickering of new windows on certain drivers. (See #97600) */
     GPU_clear_color(0.55f, 0.55f, 0.55f, 1.0f);
 
-    // GHOST_SetWindowState(ghostwin, GHOST_kWindowStateModified);
     GPU_render_end();
   }
   else {