patch 8.2.1504: Vim9: white space checks are only done for a :def function

Problem:    Vim9: white space checks are only done for a :def function.
Solution:   Also do checks at the script level.  Adjust the name of a few
            error messages.

src/vim9script.c

@@ -532,7 +532,7 @@ vim9_declare_scriptvar(exarg_T *eap, char_u *arg)
     }
     if (!VIM_ISWHITE(p[1]))
     {
-	semsg(_(e_white_space_required_after), ":");
+	semsg(_(e_white_space_required_after_str), ":");
 	return arg + STRLEN(arg);
     }
     name = vim_strnsave(arg, p - arg);