Migrate Tasks in the NuGet repo to the new Task type

NuGet tasks run in every restore. Many of them keep cached state in static members, which is not safe when projects share a process, so migrating them needs real rework rather than just an attribute.

The tasks are migrated: 18 of 21 NuGet tasks enlightened (86%). What is left would be migrated on demand if telemetry or perf tests would show its benefit.

## Steps

- [x] Migrate the NuGet tasks [size L]
- [ ] Migrate the remaining tasks [size M]

## Stakeholders

Everyone running `dotnet restore`, or a build that restores, which is nearly every build.

## Definition of done

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

Original description

Specific things to consider

* how to manage the cached state (static members) that many NuGet Tasks use
* if Graph Restore can be moved to use Net TaskHost instead of the Exec of a separate binary today.
* for the Restore task specifically - if it's in-proc can it do better multithreading?

Looks like there are [6 specific Tasks](https://github.com/search?q=repo%3ANuGet%2FNuGet.Client+%28%22%3A+Task%22+OR+%22ICancelableTask%22%29+path%3Asrc%2FNuGet.Core%2FNuGet.Build.Tasks%2F*.cs&type=code).

Notes: This will not be simple enlightening mode, there will be some re-work required to rewrite these tasks more deeply