refactor/single-include: ui.h, ui_bridge.h, ugrid.h (#6571)

src/nvim/CMakeLists.txt

@@ -448,9 +448,6 @@ set(NO_SINGLE_CHECK_HEADERS
   tag.h
   terminal.h
   tui/tui.h
-  ugrid.h
-  ui.h
-  ui_bridge.h
   undo.h
   undo_defs.h
 )

src/nvim/ui.h

@@ -6,6 +6,7 @@
 #include <stdint.h>
 
 #include "api/private/defs.h"
+#include "nvim/buffer_defs.h"
 
 typedef struct {
   bool bold, underline, undercurl, italic, reverse;