Refactor embedded assets and drop unnecessary dependencies (#34692)

Benefits:

1. smaller binary size (reduces more than 1MB)
2. better control of the assets details
3. fewer unmaintained dependencies
4. faster startup if the assets are not needed
5. won't hang up editors when open "bindata.go" by accident

modules/templates/static.go

@@ -1,22 +0,0 @@
-// Copyright 2016 The Gitea Authors. All rights reserved.
-// SPDX-License-Identifier: MIT
-
-//go:build bindata
-
-package templates
-
-import (
-	"time"
-
-	"code.gitea.io/gitea/modules/assetfs"
-	"code.gitea.io/gitea/modules/timeutil"
-)
-
-// GlobalModTime provide a global mod time for embedded asset files
-func GlobalModTime(filename string) time.Time {
-	return timeutil.GetExecutableModTime()
-}
-
-func BuiltinAssets() *assetfs.Layer {
-	return assetfs.Bindata("builtin(bindata)", Assets)
-}

modules/templates/templates_bindata.go

@@ -3,6 +3,21 @@
 
 //go:build bindata
 
+//go:generate go run ../../build/generate-bindata.go ../../templates bindata.dat
+
 package templates
 
-//go:generate go run ../../build/generate-bindata.go ../../templates templates bindata.go true
+import (
+	"sync"
+
+	_ "embed"
+
+	"code.gitea.io/gitea/modules/assetfs"
+)
+
+//go:embed bindata.dat
+var bindata []byte
+
+var BuiltinAssets = sync.OnceValue(func() *assetfs.Layer {
+	return assetfs.Bindata("builtin(bindata)", assetfs.NewEmbeddedFS(bindata))
+})