Improve template helper functions: string/slice (#24266)

Follow #23328

The improvements:

1. The `contains` functions are covered by tests
2. The inconsistent behavior of `containGeneric` is replaced by
`StringUtils.Contains` and `SliceUtils.Contains`
3. In the future we can move more help functions into XxxUtils to
simplify the `helper.go` and reduce unnecessary global functions.

FAQ:

1. Why it's called `StringUtils.Contains` but not `strings.Contains`
like Golang?

Because our `StringUtils` is not Golang's `strings` package. There will
be our own string functions.

---------

Co-authored-by: silverwind <me@silverwind.io>

modules/templates/helper.go

@@ -15,7 +15,6 @@ import (
 	"mime"
 	"net/url"
 	"path/filepath"
-	"reflect"
 	"regexp"
 	"strings"
 	"time"
@@ -68,11 +67,15 @@ func NewFuncMap() []template.FuncMap {
 		"PathEscape":         url.PathEscape,
 		"PathEscapeSegments": util.PathEscapeSegments,
 
+		// utils
+		"StringUtils": NewStringUtils,
+		"SliceUtils":  NewSliceUtils,
+
 		// -----------------------------------------------------------------
 		// string / json
+		// TODO: move string helper functions to StringUtils
 		"Join":           strings.Join,
 		"DotEscape":      DotEscape,
-		"HasPrefix":      strings.HasPrefix,
 		"EllipsisString": base.EllipsisString,
 		"DumpVar":        dumpVar,
 
@@ -144,35 +147,6 @@ func NewFuncMap() []template.FuncMap {
 			return fmt.Sprint(time.Since(startTime).Nanoseconds()/1e6) + "ms"
 		},
 
-		// -----------------------------------------------------------------
-		// slice
-		"containGeneric": func(arr, v interface{}) bool {
-			arrV := reflect.ValueOf(arr)
-			if arrV.Kind() == reflect.String && reflect.ValueOf(v).Kind() == reflect.String {
-				return strings.Contains(arr.(string), v.(string))
-			}
-			if arrV.Kind() == reflect.Slice {
-				for i := 0; i < arrV.Len(); i++ {
-					iV := arrV.Index(i)
-					if !iV.CanInterface() {
-						continue
-					}
-					if iV.Interface() == v {
-						return true
-					}
-				}
-			}
-			return false
-		},
-		"contain": func(s []int64, id int64) bool {
-			for i := 0; i < len(s); i++ {
-				if s[i] == id {
-					return true
-				}
-			}
-			return false
-		},
-
 		// -----------------------------------------------------------------
 		// setting
 		"AppName": func() string {