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/comment.go

@@ -1272,10 +1272,9 @@ func InsertIssueComments(ctx context.Context, comments []*Comment) error {
 		return nil
 	}
 
-	issueIDs := make(container.Set[int64])
-	for _, comment := range comments {
-		issueIDs.Add(comment.IssueID)
-	}
+	issueIDs := container.FilterSlice(comments, func(comment *Comment) (int64, bool) {
+		return comment.IssueID, true
+	})
 
 	ctx, committer, err := db.TxContext(ctx)
 	if err != nil {
@@ -1298,7 +1297,7 @@ func InsertIssueComments(ctx context.Context, comments []*Comment) error {
 		}
 	}
 
-	for issueID := range issueIDs {
+	for _, issueID := range issueIDs {
 		if _, err := db.Exec(ctx, "UPDATE issue set num_comments = (SELECT count(*) FROM comment WHERE issue_id = ? AND `type`=?) WHERE id = ?",
 			issueID, CommentTypeComment, issueID); err != nil {
 			return err