patch 8.2.1897: command modifiers are saved and set inconsistently

Problem:    Command modifiers are saved and set inconsistently.
Solution:   Separate parsing and applying command modifiers.  Save values in
            cmdmod_T.

src/ex_cmds.h

@@ -1883,12 +1883,6 @@ struct exarg
     void	*cookie;	// argument for getline()
 #ifdef FEAT_EVAL
     cstack_T	*cstack;	// condition stack for ":if" etc.
-#endif
-    long	verbose_save;	 // saved value of p_verbose
-    int		save_msg_silent; // saved value of msg_silent
-    int		did_esilent;	 // how many times emsg_silent was incremented
-#ifdef HAVE_SANDBOX
-    int		did_sandbox;	// when TRUE did ++sandbox
 #endif
 };