Add container.FilterSlice function (#30339)

Many places have the following logic:
```go
func (jobs ActionJobList) GetRunIDs() []int64 {
	ids := make(container.Set[int64], len(jobs))
	for _, j := range jobs {
		if j.RunID == 0 {
			continue
		}
		ids.Add(j.RunID)
	}
	return ids.Values()
}
```

this introduces a `container.FilterMapUnique` function, which reduces
the code above to:
```go
func (jobs ActionJobList) GetRunIDs() []int64 {
	return container.FilterMapUnique(jobs, func(j *ActionRunJob) (int64, bool) {
		return j.RunID, j.RunID != 0
	})
}
```

models/issues/reaction.go

@@ -305,14 +305,12 @@ func (list ReactionList) GroupByType() map[string]ReactionList {
 }
 
 func (list ReactionList) getUserIDs() []int64 {
-	userIDs := make(container.Set[int64], len(list))
-	for _, reaction := range list {
+	return container.FilterSlice(list, func(reaction *Reaction) (int64, bool) {
 		if reaction.OriginalAuthor != "" {
-			continue
+			return 0, false
 		}
-		userIDs.Add(reaction.UserID)
-	}
-	return userIDs.Values()
+		return reaction.UserID, true
+	})
 }
 
 func valuesUser(m map[int64]*user_model.User) []*user_model.User {