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.

models/user.go

@@ -141,20 +141,13 @@ func DeleteUser(ctx context.Context, u *user_model.User, purge bool) (err error)
 				break
 			}
 			for _, p := range protections {
-				var matched1, matched2, matched3 bool
-				if len(p.WhitelistUserIDs) != 0 {
-					p.WhitelistUserIDs, matched1 = util.RemoveIDFromList(
-						p.WhitelistUserIDs, u.ID)
-				}
-				if len(p.ApprovalsWhitelistUserIDs) != 0 {
-					p.ApprovalsWhitelistUserIDs, matched2 = util.RemoveIDFromList(
-						p.ApprovalsWhitelistUserIDs, u.ID)
-				}
-				if len(p.MergeWhitelistUserIDs) != 0 {
-					p.MergeWhitelistUserIDs, matched3 = util.RemoveIDFromList(
-						p.MergeWhitelistUserIDs, u.ID)
-				}
-				if matched1 || matched2 || matched3 {
+				lenIDs, lenApprovalIDs, lenMergeIDs := len(p.WhitelistUserIDs), len(p.ApprovalsWhitelistUserIDs), len(p.MergeWhitelistUserIDs)
+				p.WhitelistUserIDs = util.SliceRemoveAll(p.WhitelistUserIDs, u.ID)
+				p.ApprovalsWhitelistUserIDs = util.SliceRemoveAll(p.ApprovalsWhitelistUserIDs, u.ID)
+				p.MergeWhitelistUserIDs = util.SliceRemoveAll(p.MergeWhitelistUserIDs, u.ID)
+				if lenIDs != len(p.WhitelistUserIDs) ||
+					lenApprovalIDs != len(p.ApprovalsWhitelistUserIDs) ||
+					lenMergeIDs != len(p.MergeWhitelistUserIDs) {
 					if _, err = e.ID(p.ID).Cols(
 						"whitelist_user_i_ds",
 						"merge_whitelist_user_i_ds",