Moves BE web ide terminal and file sync to core

What does this MR do?

Refs #211685 (closed) and #211686 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [ ] Changelog entry
• [ ] Documentation ([if required](https://docs.gitlab.com/ee/development/documentation/workflow.html#when-documentation-is-required))
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content