Migrate Arcade tasks to the new Task type

Arcade tasks run in every VMR and .NET repo build. Until they are migrated, an `-mt` build sends them to a separate task host process, which cancels out much of the benefit of multithreaded mode. This is a prerequisite for dogfooding multithreaded mode in the VMR.

## Steps

- [ ] Migrate the Arcade tasks [size L]

## Stakeholders

The VMR and every repo that builds with Arcade.

## Definition of done

Every Arcade task either runs in multithreaded mode, or is recorded as intentionally left out.

Start by locating the Arcade task definitions used by the VMR and .NET repository builds, then inspect how -mt builds route those tasks and how the new Task type is used. Done means every Arcade task runs in multithreaded mode or is explicitly recorded as intentionally excluded.

Written by the indexing model from the issue text.