Allow commits to be queried by repository using the `tagged(...)` typehaead function
Summary:
Fixes T12322. Allows you to search for commits using the `tagged(...)` repository function, so you can find "any commmit in any repository tagged with android" or similar.
I moved the function from Differential (which was the application using it) to Diffusion (which is more accurately the application which provides it).
I fixed a bug where searching for `tagged(xyz)` would have no effect (constraint was ignored) if there were no repositories tagged with "xyz". The fix isn't perfectly clean, but should work properly for the moment.
Test Plan:
- Searched with `tagged(...)` in Diffusion and Differential.
- Searched by repository.
- Searched with `tagged(...)` for a project with no tagged repositories.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T12322
Differential Revision: https://secure.phabricator.com/D17426