Improve utils of slices (#22379)

- Move the file `compare.go` and `slice.go` to `slice.go`.
- Fix `ExistsInSlice`, it's buggy
  - It uses `sort.Search`, so it assumes that the input slice is sorted.
- It passes `func(i int) bool { return slice[i] == target })` to
`sort.Search`, that's incorrect, check the doc of `sort.Search`.
- Conbine `IsInt64InSlice(int64, []int64)` and `ExistsInSlice(string,
[]string)` to `SliceContains[T]([]T, T)`.
- Conbine `IsSliceInt64Eq([]int64, []int64)` and `IsEqualSlice([]string,
[]string)` to `SliceSortedEqual[T]([]T, T)`.
- Add `SliceEqual[T]([]T, T)` as a distinction from
`SliceSortedEqual[T]([]T, T)`.
- Redesign `RemoveIDFromList([]int64, int64) ([]int64, bool)` to
`SliceRemoveAll[T]([]T, T) []T`.
- Add `SliceContainsFunc[T]([]T, func(T) bool)` and
`SliceRemoveAllFunc[T]([]T, func(T) bool)` for general use.
- Add comments to explain why not `golang.org/x/exp/slices`.
- Add unit tests.

routers/web/repo/issue.go

@@ -139,7 +139,7 @@ func issues(ctx *context.Context, milestoneID, projectID int64, isPullOption uti
 	viewType := ctx.FormString("type")
 	sortType := ctx.FormString("sort")
 	types := []string{"all", "your_repositories", "assigned", "created_by", "mentioned", "review_requested"}
-	if !util.IsStringInSlice(viewType, types, true) {
+	if !util.SliceContainsString(types, viewType, true) {
 		viewType = "all"
 	}
 
@@ -3087,7 +3087,7 @@ func updateAttachments(ctx *context.Context, item interface{}, files []string) e
 		return fmt.Errorf("unknown Type: %T", content)
 	}
 	for i := 0; i < len(attachments); i++ {
-		if util.IsStringInSlice(attachments[i].UUID, files) {
+		if util.SliceContainsString(files, attachments[i].UUID) {
 			continue
 		}
 		if err := repo_model.DeleteAttachment(attachments[i], true); err != nil {