Arpow: GenerateFileFromTemplate task causes BuildTools prebuilt

[dseefeld]

Describe the bug

The GenerateFileFromTemplate task is defined in BuildTools, which isn't built with source-build. This will be reported as a prebuilt in Arpow when building offline and when prebuilt reporting is turned on. This task should either be moved to Arcade or moved into RepoTasks to ensure it can build and be used with source-build.

To Reproduce

When Arpow source-build CI is included (see #31445), in the generated results (Microsoft.SourceBuild.Intermediate.aspnetcore.*.nupkg), the file prebuilt-report/annotated-usage.xml will contain a reference to BuildTools, indicating that this is a prebuilt.

[dougbu]

Resolution requires dotnet/arcade#7403 and adoption of the new package in this repo. Assigning to @JunTaoLuo since he owns at least the first (larger) part of this.