patch 8.2.3190: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move error messages to errors.h and give them a clear name.
diff --git a/src/regexp.c b/src/regexp.c
index 805056e..5a17d24 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -1359,7 +1359,7 @@
 
     if (UCHARAT(((bt_regprog_T *)prog)->program) != REGMAGIC)
     {
-	emsg(_(e_re_corr));
+	emsg(_(e_corrupted_regexp_program));
 	return TRUE;
     }
     return FALSE;
@@ -1982,7 +1982,7 @@
     // Be paranoid...
     if ((source == NULL && expr == NULL) || dest == NULL)
     {
-	emsg(_(e_null));
+	emsg(_(e_null_argument));
 	return 0;
     }
     if (prog_magic_wrong())
@@ -2289,7 +2289,7 @@
 		    else if (*s == NUL) // we hit NUL.
 		    {
 			if (copy)
-			    iemsg(_(e_re_damg));
+			    iemsg(_(e_damaged_match_string));
 			goto exit;
 		    }
 		    else