CE Backport: Add library helpers to use in Roadmap

What does this MR do?

This MR backports ~backstage changes from EE MR https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9018 into CE by doing following changes;

Adds following helper methods;

• newDate within app/assets/javascripts/lib/utils/datetime_utility.js.

Updates following helpers;

• getTimeframeWindowFrom within app/assets/javascripts/lib/utils/datetime_utility.js.
• isInViewport within app/assets/javascripts/lib/utils/common_utils.js.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/7325

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added, if necessary
• [ ] Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• ~~[ ] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.~~
• Security reports checked/validated by reviewer