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.

services/auth/source/ldap/source_search.go

@@ -246,7 +246,7 @@ func (source *Source) getMappedMemberships(l *ldap.Conn, uid string) (map[string
 	membershipsToAdd := map[string][]string{}
 	membershipsToRemove := map[string][]string{}
 	for group, memberships := range ldapGroupsToTeams {
-		isUserInGroup := util.IsStringInSlice(group, usersLdapGroups)
+		isUserInGroup := util.SliceContainsString(usersLdapGroups, group)
 		if isUserInGroup {
 			for org, teams := range memberships {
 				membershipsToAdd[org] = teams