[RDY] Move some types and consts from structs.h to other files

- `garray_T` to `garray.h` 
- `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`