Move some types and consts from structs.h to other headers

- `foldinfo_T` to `fold.h`
 - `context_sha256_T` to `sha256.h`
 - `tagname_T` to `tag.h`
 - `pumitem_T` to `popupmnu.h`
 - `prt_*_T` to  hardcopy.h`
 - `CPT_*` consts to `edit.h`
 - `vimmenu_T`, `MNU_HIDDEN_CHAR`, and `MENU_*` constants to `menu.h`

src/globals.h

@@ -10,6 +10,7 @@
 #define NEOVIM_GLOBALS_H
 
 #include "mbyte.h"
+#include "menu.h"
 
 /*
  * definition of global variables