tstest/deptest: add check that x/exp/{maps,slices} imported as xfoo

Updates #cleanup

Change-Id: I4cbb5e477c739deddf7a46b66f286c9fdb106279
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/deptest/deptest_test.go

@@ -0,0 +1,10 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package deptest
+
+import "testing"
+
+func TestImports(t *testing.T) {
+	ImportAliasCheck(t, "../../")
+}