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/buffer.c b/src/buffer.c
index 60aa32f..25efea1 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1942,7 +1942,7 @@
 	emsg(_("E948: Job still running (add ! to end the job)"));
     else
 #endif
-	emsg(_("E37: No write since last change (add ! to override)"));
+	emsg(_(e_no_write_since_last_change_add_bang_to_override));
 }
 
     void
@@ -1953,7 +1953,7 @@
 	emsg(_("E948: Job still running"));
     else
 #endif
-	emsg(_("E37: No write since last change"));
+	emsg(_(e_no_write_since_last_change));
 }
 
 /*