R1:e8142915269a

Introduce ManiphestTaskSearchEngine plus ManiphestTaskListControllerPro

Summary:
Ref T603. Ref T2625. Cutting this over is tricky because of Maniphest's existing saved queries. Plan here is:

- Build out the "pro" controller at `/maniphest/query/`.
- Once it's at parity, migrate custom queries.
- Nuke the old UI.

This provides a minimal implementation with no filter support.

Test Plan: Looked at `/maniphest/query/`, saw results technically available.

Reviewers: btrahan

Reviewed By: btrahan

CC…