Clarify that desktop mode is the non-exclusive borderless fullscreen mode

Fixes https://github.com/libsdl-org/SDL/issues/8413

docs/README-migration.md

@@ -1509,7 +1509,7 @@ SDL_GetDesktopDisplayMode() and SDL_GetCurrentDisplayMode() return pointers to d
 
 Windows now have an explicit fullscreen mode that is set, using SDL_SetWindowFullscreenMode(). The fullscreen mode for a window can be queried with SDL_GetWindowFullscreenMode(), which returns a pointer to the mode, or NULL if the window will be fullscreen desktop. SDL_SetWindowFullscreen() just takes a boolean value, setting the correct fullscreen state based on the selected mode.
 
-SDL_WINDOW_FULLSCREEN_DESKTOP has been removed, and you can call SDL_GetWindowFullscreenMode() to see whether an exclusive fullscreen mode will be used or the fullscreen desktop mode will be used when the window is fullscreen.
+SDL_WINDOW_FULLSCREEN_DESKTOP has been removed, and you can call SDL_GetWindowFullscreenMode() to see whether an exclusive fullscreen mode will be used or the borderless fullscreen desktop mode will be used when the window is fullscreen.
 
 SDL_SetWindowBrightness and SDL_SetWindowGammaRamp have been removed from the API, because they interact poorly with modern operating systems and aren't able to limit their effects to the SDL window.
 

include/SDL3/SDL_video.h

@@ -654,8 +654,8 @@ extern DECLSPEC float SDLCALL SDL_GetWindowDisplayScale(SDL_Window *window);
  *
  * \param window the window to affect
  * \param mode a pointer to the display mode to use, which can be NULL for
- *             desktop mode, or one of the fullscreen modes returned by
- *             SDL_GetFullscreenDisplayModes().
+ *             borderless fullscreen desktop mode, or one of the fullscreen modes returned by
+ *             SDL_GetFullscreenDisplayModes() to set an exclusive fullscreen mode.
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *
@@ -671,7 +671,7 @@ extern DECLSPEC int SDLCALL SDL_SetWindowFullscreenMode(SDL_Window *window, cons
  * Query the display mode to use when a window is visible at fullscreen.
  *
  * \param window the window to query
- * \returns a pointer to the fullscreen mode to use or NULL for desktop mode
+ * \returns a pointer to the exclusive fullscreen mode to use or NULL for borderless fullscreen desktop mode
  *
  * \since This function is available since SDL 3.0.0.
  *
@@ -1608,8 +1608,8 @@ extern DECLSPEC int SDLCALL SDL_RestoreWindow(SDL_Window *window);
 /**
  * Request that the window's fullscreen state be changed.
  *
- * By default a window in fullscreen state uses fullscreen desktop mode, but a
- * specific display mode can be set using SDL_SetWindowFullscreenMode().
+ * By default a window in fullscreen state uses borderless fullscreen desktop mode, but a
+ * specific exclusive display mode can be set using SDL_SetWindowFullscreenMode().
  *
  * On some windowing systems this request is asynchronous and the new
  * fullscreen state may not have have been applied immediately upon the return