refactor: move some anonymous enums back to non-defs headers (#26622)

It isn't really useful to put anonymous enums only used as arguments to
functions calls in _defs.h headers, as they will only be used by a file
that calls those functions, which requires including a non-defs header.

Also move os_msg() and os_errmsg() back to message.h, as on Windows they
are actual functions instead of macros.

Also remove gettext.h and globals.h from private/helpers.h.

src/nvim/ex_cmds_defs.h

@@ -230,24 +230,6 @@ typedef struct {
   } magic;
 } CmdParseInfo;
 
-/// flags for do_ecmd()
-enum {
-  ECMD_HIDE       = 0x01,  ///< don't free the current buffer
-  ECMD_SET_HELP   = 0x02,  ///< set b_help flag of (new) buffer before opening file
-  ECMD_OLDBUF     = 0x04,  ///< use existing buffer if it exists
-  ECMD_FORCEIT    = 0x08,  ///< ! used in Ex command
-  ECMD_ADDBUF     = 0x10,  ///< don't edit, just add to buffer list
-  ECMD_ALTBUF     = 0x20,  ///< like ECMD_ADDBUF and set the alternate file
-  ECMD_NOWINENTER = 0x40,  ///< do not trigger BufWinEnter
-};
-
-/// for lnum argument in do_ecmd()
-enum {
-  ECMD_LASTL = 0,   ///< use last position in loaded file
-  ECMD_LAST  = -1,  ///< use last position in all files
-  ECMD_ONE   = 1,   ///< use first line
-};
-
 /// Previous :substitute replacement string definition
 typedef struct {
   char *sub;            ///< Previous replacement string.