patch 8.2.3975: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/window.c b/src/window.c
index 3784368..ef35a86 100644
--- a/src/window.c
+++ b/src/window.c
@@ -774,7 +774,7 @@
 {
     if (split_disallowed > 0)
     {
-	emsg(_("E242: Can't split a window while closing another"));
+	emsg(_(e_cant_split_window_while_closing_another));
 	return FAIL;
     }
     if (curwin->w_buffer->b_locked_split)