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/vim.h b/src/vim.h
index 6377dab..2b28948 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2179,6 +2179,7 @@
 #endif
 
 #include "globals.h"	    // global variables and messages
+#include "errors.h"	    // error messages
 
 /*
  * If console dialog not supported, but GUI dialog is, use the GUI one.