Tasks can be searched with task id in differential Task Selector

Summary:

Task selector didn't support searching tasks with their IDs, e.g., 'T17'.
This was confusing, because in the task list the task ID was visible, but you
could not search them.

Test Plan:

• Checked that searching 'T<task_id>' works with all the filters
• Checked that using multiple task IDs in the same query works
• Check that mixing task IDs and free text works

Reviewers: epriestley

CC: jungejason

Differential Revision: 105