Rename utils/worker to tree_worker_utils

What does this MR do?

This MR renames utils/workers.js module to utils/tree_worker_utils.js.

Why?

workers is a bit ambiguous and sounds like these might be utils for creating/managing workers. 🤷

The only module actually using these functions is tree_worker.js so I opted to just keep it explicit like that.

Does this MR meet the acceptance criteria?

Conformity

• [ ] I have included a changelog entry, or it's not needed. (Does this MR need a changelog?) Not needed since no user facing changes.
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.