refactor: remove some unused includes (#19820)

Replace grid.h in screen.h and screen.h in buffer.h with grid_defs.h

src/nvim/api/buffer.c

@@ -28,6 +28,7 @@
 #include "nvim/memory.h"
 #include "nvim/move.h"
 #include "nvim/ops.h"
+#include "nvim/screen.h"
 #include "nvim/undo.h"
 #include "nvim/vim.h"
 #include "nvim/window.h"

src/nvim/api/ui.c

@@ -11,6 +11,7 @@
 #include "nvim/api/ui.h"
 #include "nvim/channel.h"
 #include "nvim/cursor_shape.h"
+#include "nvim/grid.h"
 #include "nvim/highlight.h"
 #include "nvim/map.h"
 #include "nvim/memory.h"
@@ -18,7 +19,6 @@
 #include "nvim/msgpack_rpc/helpers.h"
 #include "nvim/option.h"
 #include "nvim/popupmnu.h"
-#include "nvim/screen.h"
 #include "nvim/ui.h"
 #include "nvim/vim.h"
 #include "nvim/window.h"

src/nvim/api/vim.c

@@ -34,6 +34,7 @@
 #include "nvim/fileio.h"
 #include "nvim/getchar.h"
 #include "nvim/globals.h"
+#include "nvim/grid.h"
 #include "nvim/highlight.h"
 #include "nvim/highlight_defs.h"
 #include "nvim/highlight_group.h"