Refactor: func StringInSlice to slices.Contains (#24262)

* Refactor: Use generic to change func StringInSlice to Contains

* Refactor: Use generic to change func stringNotInSlice to Contains

Make utils.go (dir server/public/utils) and func Contains

* Refactor: Move func Contains from channels/utils to public/utils

Move func Contains from channels/utils to public/utils

Fix import declarations line

* Docs: Add a description of the Contains function

* Test: add TestContains

Add a test code for a Contain function

server/channels/app/notification_test.go

@@ -13,8 +13,9 @@ import (
 
 	"github.com/mattermost/mattermost/server/public/model"
 	"github.com/mattermost/mattermost/server/public/shared/i18n"
+	pUtils "github.com/mattermost/mattermost/server/public/utils"
+
 	"github.com/mattermost/mattermost/server/v8/channels/store"
-	"github.com/mattermost/mattermost/server/v8/channels/utils"
 )
 
 func getLicWithSkuShortName(skuShortName string) *model.License {
@@ -49,7 +50,7 @@ func TestSendNotifications(t *testing.T) {
 	mentions, err := th.App.SendNotifications(th.Context, post1, th.BasicTeam, th.BasicChannel, th.BasicUser, nil, true)
 	require.NoError(t, err)
 	require.NotNil(t, mentions)
-	require.True(t, utils.StringInSlice(th.BasicUser2.Id, mentions), "mentions", mentions)
+	require.True(t, pUtils.Contains(mentions, th.BasicUser2.Id), "mentions", mentions)
 
 	t.Run("license is required for group mention", func(t *testing.T) {
 		group := th.CreateGroup()
@@ -145,7 +146,7 @@ func TestSendNotifications(t *testing.T) {
 			}
 			mentions, err = th.App.SendNotifications(th.Context, childPost, th.BasicTeam, th.BasicChannel, th.BasicUser2, &postList, true)
 			require.NoError(t, err)
-			require.False(t, utils.StringInSlice(user.Id, mentions))
+			require.False(t, pUtils.Contains(mentions, user.Id))
 		}
 
 		th.BasicUser.NotifyProps[model.CommentsNotifyProp] = model.CommentsNotifyAny
@@ -2815,7 +2816,7 @@ func TestReplyPostNotificationsWithCRT(t *testing.T) {
 		}
 		mentions, err := th.App.SendNotifications(th.Context, childPost, th.BasicTeam, th.BasicChannel, th.BasicUser2, &postList, true)
 		require.NoError(t, err)
-		assert.False(t, utils.StringInSlice(user.Id, mentions))
+		assert.False(t, pUtils.Contains(mentions, user.Id))
 
 		membership, err := th.App.GetThreadMembershipForUser(user.Id, rootPost.Id)
 		assert.Error(t, err)