WIP: Resolve "Issuable search filter wrongly recognize tokens"

What does this MR do?

TODO:

• fails for some pasted strings
• should potentially change processTokens function, and simplify the handler in filtered_search_manager

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #36210 (moved)