patch 8.2.1444: error messages are spread out and names can be confusing

Problem:    Error messages are spread out and names can be confusing.
Solution:   Start moving error messages to a separate file and use clear
            names.
diff --git a/src/vim9script.c b/src/vim9script.c
index e7bb433..c13da69 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -513,7 +513,7 @@
 
     if (eap->cmdidx == CMD_const)
     {
-	emsg(_(e_const_req_value));
+	emsg(_(e_const_requires_a_value));
 	return arg + STRLEN(arg);
     }
 
@@ -530,12 +530,12 @@
 
     if (*p != ':')
     {
-	emsg(_(e_type_req));
+	emsg(_(e_type_or_initialization_required));
 	return arg + STRLEN(arg);
     }
     if (!VIM_ISWHITE(p[1]))
     {
-	semsg(_(e_white_after), ":");
+	semsg(_(e_white_space_required_after), ":");
 	return arg + STRLEN(arg);
     }
     name = vim_strnsave(arg, p - arg);