patch 8.2.3983: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/regexp_bt.c b/src/regexp_bt.c
index 076a74d..2af1f56 100644
--- a/src/regexp_bt.c
+++ b/src/regexp_bt.c
@@ -2517,7 +2517,7 @@
     {
 	vim_free(r);
 	if (reg_toolong)
-	    EMSG_RET_NULL(_("E339: Pattern too long"));
+	    EMSG_RET_NULL(_(e_pattern_too_long));
 	return NULL;
     }