patch 8.2.3750: error messages are everywhere

Problem:    Error messages are everywhere.
Solution:   Move more error messages to errors.h and adjust the names.
diff --git a/src/session.c b/src/session.c
index d2b360d..e64697f 100644
--- a/src/session.c
+++ b/src/session.c
@@ -1331,7 +1331,7 @@
 	failed |= fclose(fd);
 
 	if (failed)
-	    emsg(_(e_write));
+	    emsg(_(e_error_while_writing));
 #if defined(FEAT_SESSION)
 	else if (eap->cmdidx == CMD_mksession)
 	{