Use the bgCoroutineContext to update note shortcut

- Application scope is using Dispatchers.Main.immediate causing ANRs
  when updating note-taking shortcuts. So using bgCoroutineContext when
  when updating note-tasks.
- Internally bgCoroutineContext uses Dispatchers.IO which should help
  avoid the ANR in SysUI.
- Using the new CoroutineScope.launch function that supports tracing to
  help debug future potential ANRs.

Bug: 311325103
Test: atest NoteTaskControllerTest
Flag: NA
Change-Id: I179d49285c7184200e11754fc0c735c55d1ed0d0