Add generic set type (#21408)

This PR adds a generic set type to get rid of maps used as sets.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/container/set_test.go

@@ -0,0 +1,37 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package container
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSet(t *testing.T) {
+	s := make(Set[string])
+
+	assert.True(t, s.Add("key1"))
+	assert.False(t, s.Add("key1"))
+	assert.True(t, s.Add("key2"))
+
+	assert.True(t, s.Contains("key1"))
+	assert.True(t, s.Contains("key2"))
+	assert.False(t, s.Contains("key3"))
+
+	assert.True(t, s.Remove("key2"))
+	assert.False(t, s.Contains("key2"))
+
+	assert.False(t, s.Remove("key3"))
+
+	s.AddMultiple("key4", "key5")
+	assert.True(t, s.Contains("key4"))
+	assert.True(t, s.Contains("key5"))
+
+	s = SetOf("key6", "key7")
+	assert.False(t, s.Contains("key1"))
+	assert.True(t, s.Contains("key6"))
+	assert.True(t, s.Contains("key7"))
+}