Expose public/ API as submodule (#23345)

* model -> public/model

* plugin -> public/plugin

* public/model/utils -> public/utils

* platform/shared/mlog -> public/shared/mlog

* platform/shared/i18n -> public/shared/i18n

* platform/shared/markdown -> public/shared/markdown

* platform/services/timezones -> public/shared/timezones

* channels/einterfaces -> einterfaces

* expose public/ submodule

* go mod tidy

* .github: cache-dependency-path, setup-go-work

* modules-tidy for public/ too

* remove old gomodtidy

server/public/plugin/checker/check_api_test.go

@@ -0,0 +1,60 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package main
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCheckAPIVersionComments(t *testing.T) {
+	testCases := []struct {
+		name, pkgPath, err string
+		expected           result
+	}{
+		{
+			name:    "valid comments",
+			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/valid",
+			err:     "",
+		},
+		{
+			name:    "invalid comments",
+			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/invalid",
+			expected: result{
+				Errors: []string{"internal/test/invalid/invalid.go:15:2: missing a minimum server version comment on method InvalidMethod"},
+			},
+		},
+		{
+			name:    "missing API interface",
+			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/missing",
+			err:     "could not find API interface",
+		},
+		{
+			name:    "non-existent package path",
+			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/does_not_exist",
+			err:     "could not find API interface",
+		},
+	}
+
+	// Enable debug flag to have packagesdriver/sizes.go print stderr of `go list` command.
+	// We want to surface any error text that may exist in stderr of this command.
+	prevEnvValue := os.Getenv("GOPACKAGESPRINTGOLISTERRORS")
+	os.Setenv("GOPACKAGESPRINTGOLISTERRORS", "true")
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			res, err := checkAPIVersionComments(tc.pkgPath)
+			assert.Equal(t, res, tc.expected)
+
+			if tc.err != "" {
+				assert.EqualError(t, err, tc.err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+	os.Setenv("GOPACKAGESPRINTGOLISTERRORS", prevEnvValue)
+}