Use ShellExecutor when interacting with TaskViewTransitions

A couple of methods in TaskViewTaskController are coming from
TaskViewTransitions so I think those are fine as is, but a couple
of places are coming from users of TaskView, so update those spots
to run on ShellExecutor.

Test: treehugger / manually tried bubbles & home controls
Bug: 290795301
Change-Id: Idf773e700873bfaf2688fff6ae1f95b43767eb99